Photosensitive ceramic composite and method for manufacturing multilayer substrate including the composite

ABSTRACT

The present invention relates to a photosensitive ceramic composite and a method for manufacturing a multilayer substrate using the composite. The photosensitive ceramic composite and manufacturing method of the present invention are applicable to circuit members and components for ceramic multilayer substrates for high-frequency wireless communication.  
     The photosensitive ceramic composite contains inorganic particles and a photosensitive organic component. The inorganic particles have at least surface sections containing an inorganic material having a refractive index less than that of inner sections of the inorganic particles.

TECHNICAL FIELD

[0001] The present invention relates to a photosensitive ceramiccomposite and a method for manufacturing a multilayer substrate usingthe composite. The ceramic multilayer substrate and manufacturing methodof the present invention are applicable to circuit members andcomponents of ceramic multilayer substrates for high-frequency wirelesscommunication.

BACKGROUND ART

[0002] Wireless communication technology including cellular phones hasbeen widely used. Known cellular phones use a quasi-microwave band witha range of 800 MHz to 1.5 GHz. However, since the information contenthas been increased, wireless communication techniques using carrierfrequencies in the millimeter wave band, which is higher than themicrowave band, have been proposed and are in practical use. Wirelesscommunication circuits for such high frequencies are expected to be usedfor mobile communications and network devices and increased inimportance because such circuits are used Bluetooth and ITS (IntelligentTransport System).

[0003] In order to achieve the high-frequency circuits, materials forsubstrates included in the circuits must have superior high-frequencypropagation characteristics at desired frequencies, that is, 1 to 100GHz. In particular, ceramic substrates have attracted much attentionbecause the following requirements are necessary to obtain suchhigh-frequency propagation characteristics: low dielectric loss, highprocessing accuracy, and high dimensional stability.

[0004] However, known materials for ceramic substrates have highdimensional stability but low micro-processing accuracy; hence,satisfactory characteristics cannot be obtained at high frequencies. Inorder to improve the microprocessing accuracy, the following techniqueis disclosed in Japanese Unexamined Patent Application Publication No.6-202323: a technique for forming via-holes in a green sheet containinga photosensitive ceramic composite by a photolithographic process.However, in the technique, there is a problem in that via-holes having adiameter of 100 μm or less cannot be uniformly formed in the sheethaving a high aspect ratio, for example, a thickness of more than 50 μmin an accurate manner because the photosensitive ceramic composite haslow sensitivity and resolution.

[0005] Since known photo-cured photosensitive green sheets have lowelongation and tensile strength, there is a problem in that the sheetsare damaged in sheet-handling steps such as a step of forming via-holesin the sheets peeled off from a film, a step of filling the via-holeswith conductive paste, a step of forming a conductive pattern on thesheets, and a step of stacking the resulting sheets.

[0006] A process for preparing multilayer substrates using a ceramicmaterial includes a step of forming via-holes in ceramic green sheets; astep of filling the via-holes with conductive paste or conductive metalpowder; a step of forming a conductive pattern, for forming electrodesand/or circuits, on the resulting sheets; a step of stacking the sheetshaving the via-holes and conductive pattern to press the resultingsheets to form a green compact; a step of cutting the green compact intopieces, having a desired size, for preparing the substrate; and a stepof firing the obtained pieces. In the firing step, the pieces are shrunkby 10% to 20%. Since the shrinkage is not necessarily uniform, thedimensional accuracy is lowered and the yield is therefore reduced.

[0007] On the other hand, substrates for circuits principally used forhigh-frequency wireless communication are used to manufacture mobileapparatuses as described above. Therefore, in order to increase thewiring density, the accuracy of processing via-holes must be enhancedand the diameter of the via-holes must be reduced. In addition, theshape and volume of modules including components are limited when themodules are placed in housings of the mobile apparatuses. Furthermore,since the directivity and sensitivity of internal antennas are greatlyvaried depending on the shape of a dielectric material, the degree offreedom in trimming must be high. However, since ceramic materials arehard and brittle, the trimming thereof seems to be difficult and hasbeen hardly tried due to the low machinability.

[0008] The technique for processing the via-holes in the ceramicsubstrate by a photolithographic process has been disclosed as describedabove. However, in order to reduce the size of the mobile apparatuses,demands for microprocessing are increased; hence outer regions ofpackages must be machined.

[0009] The following apparatuses usually include glass ceramicmultilayer substrates in principle for the above reasons: compactwireless terminals such as cellular phones and PDA (Personal DigitalAssistance), image information systems such as digital video cameras andnavigation systems for automobiles, and personal computers having awireless communication function. In those apparatuses, there are manyrequirements for the package shape in view of the portability, thereduction in size, and the resistance to physical impact. This isbecause the following problems must be prevented since the portabilityand the reduction in size are demanded: a decrease in packaging volumeavailable in the apparatuses, irregularities inside housing members, andinterference between other components and modules.

[0010] A current technique for trimming sheets usually uses an NCpunching machine or a die and has the problems below.

[0011] (1) A punching process using such an NC punching machine causesan increase in time to form continuous cutting lines.

[0012] (2) A punching process using such a die gives high productivitybut causes an increase in cost because of the preparation of dies thatcan cope with arbitral shapes. The process also causes an increase inthe number of manufacturing steps because a new die must be preparedwhen the substrate design is slightly modified.

[0013] (3) As is common with the NC punching machine and the die, thediameter of through-holes and via-holes is 0.1 mm or more because theminimum diameter of pins is about 0.1 mm. Therefore, the reproducibilityof the shape is unsatisfactory in some cases when the external shape ismachined.

[0014] (4) As is common with the NC punching machine and the die, greensheets formed on a sheet and then trimmed are isolated from each otherwhen the external shapes have independent patterns. A step of stackingthe resulting sheets is extremely complicated because the sheets must bealigned with each other, and the misalignment between the independentpatterns is large.

[0015] As described above, the known machining processes areunsatisfactory for the sheet trimming. Therefore, the followingsubstrate is proposed: a multilayer glass-ceramic substrate having anarbitrary external shape that is extremely fine and can be formed by asimple process, for example, a photolithographic process used formicroprocessing via-holes or the like on a trial basis.

[0016] When sheets are trimmed by such a photolithographic process, thesurface area of developed regions of the sheets is greatly differentfrom that of other regions in contact with a developing solution in adeveloping step as compared with the processing of the via-holes.Therefore, the swelling rate of the sheets placed in the developingsolution must be maintained constant and low. When the trimmed sheetsare stacked and then fired, warpage and distortion can occur and cracksmay be formed in some cases because stress concentration occurs in thesheets.

[0017] Since the trimmed sheets have independent patterns formed bytrimming, the sheets must be processed in steps between the developingstep and the stacking step in such a manner that the flexibility of thesheets is maintained.

[0018] In order to obtain satisfactory characteristics at highfrequencies by increasing the degree of microprocessing source materialsof ceramic substrates having high dimensional stability and a lowdielectric loss tangent, fine via-holes having a high aspect ratio mustbe formed by a photolithographic process.

[0019] Furthermore, the sheets processed or not must be in a suitablecondition fit for a step of forming a multilayer substrate in additionto the formation of such via-holes. Therefore, the photo-cured sheetsmust have an elongation, tensile modulus, and strength that aresubstantially equal to those of ordinary non-photosensitive greensheets.

[0020] A microprocessing technique using the photolithographic processis useful not only for processing the via-holes in the multilayersubstrate but also for reducing the size of modules and for enhancingthe performance. Therefore, a practical technique for processing themultilayer substrate by a photolithographic process is critical.

[0021] It is an object of the present invention to provide a ceramicmaterial that can be microprocessed by the photolithographic process andare fit for a step of stacking the sheets to prepare the multilayersubstrate as described above and also provide a new method forprocessing the multilayer substrate containing the material and acircuit substrate obtained by the method.

DISCLOSURE OF INVENTION

[0022] The present invention basically has the configuration below.

[0023] A photosensitive ceramic composite contains inorganic particlesand a photosensitive organic component, wherein the inorganic particleshave at least surface sections containing an inorganic material having arefractive index less than that of inner sections of the inorganicparticles.

[0024] The photosensitive ceramic composite has a dimensional change of1 to 1.5 in a developing step and contains the inorganic particles(component B) and the photosensitive organic component (component A)containing a (meth)acrylate compound (sub-component A1) and a urethanecompound (sub-component A2) having an ethylenic unsaturated group. The(meth)acrylate compound is represented by the following formula:

CH₂═CR¹COO—(R² )_(n)—R³—R⁰   (1)

[0025] wherein R⁰ represents a CH₂═CR¹COO—(R²)_(n)—group, a hydrogenatom, or a halogen atom; R¹ represents a hydrogen atom or a methylgroup; R² represents an alkylene oxide group or an alkylene oxideoligomer group; R³ represents a cyclic or acyclic group selected fromthe group consisting of an alkylene group, an aryl group, an aryl ethergroup, an arylene group, an arylene ether group, an aralkyl group, andan aralkylene group having 1 to 15 carbon atoms or represents such acyclic or acyclic group having a substituent such as an alkyl grouphaving 1 to 9 carbon atoms, a halogen atom, a hydroxy group, or an arylgroup; and n represents an integer of 1 to 5.

[0026] A method for manufacturing a multilayer substrate using thephotosensitive ceramic composite containing the inorganic particles andphotosensitive organic component includes the following steps:

[0027] (1) a step of forming the photosensitive ceramic composite intophotosensitive green sheets;

[0028] (2) a step of trimming the resulting photosensitive green sheetsby a photolithographic process;

[0029] (3) a step of stacking the resulting photosensitive green sheets;and

[0030] (4) a step of firing the resulting photosensitive green sheets.

[0031] Alternatively, the present invention provides a multilayersubstrate manufactured by the above method.

BEST MODE FOR CARRYING OUT THE INVENTION

[0032] A photosensitive ceramic composite of the present inventionnecessarily contains inorganic particles and a photosensitive organiccomponent. The inorganic particles must have surface sections containingan inorganic material with a refractive index less than that of innersections of the inorganic particles. In the inorganic particles, eachinner section is placed at a position deeper than that of each differentsurface material and occupies a major part of each inorganic particle,that is, the inner section almost entirely occupies the inorganicparticle other than the different surface material. The percentage ofthe different surface material in the inorganic particle is notparticularly limited and is preferably within a range of 1×10⁻⁴ to 2×10percent by weight (more preferably 1×10⁻³ to 1×10 and further morepreferably 2.5×10⁻² to 5 percent by weight). Therefore, the percentageof the inner section is substantially the remainder. When the percentageof the different surface material is outside the above range, thesection containing the different surface material described below cannothave a suitable thickness. Furthermore, when the percentage of the innersection is extremely small, the optimum performance of a ceramicmaterial obtained finally cannot be achieved in some cases. Therefore,the percentage outside the above range is not preferable.Characteristics (refractive index and the like) of the inner section canbe assumed to be substantially the same as those of the entire inorganicparticle including the different surface material in some cases. Inorder to precisely determine the characteristics of the inner section,portions of the inorganic particle may be measured for eachcharacteristic, whereby an average measurement is obtained. The particleportions are arranged in the radius direction of the inorganic particleand are 0.2×r apart from the surface (within a range of 0.2×r to r inthe depth direction), wherein r represents the radius (the distancebetween the surface and the center when the inorganic particle is notspherical) of the inorganic particle. The difference in physicalcharacteristic and/or the difference in chemical characteristic is notparticularly limited if characteristics of the photosensitive ceramiccomposite can be improved by modifying surface properties of theinorganic particle. The refractive indexes are preferably different fromeach other and small in particular as described below.

[0033] The formula 5≦t ≦200 (nm) is preferably satisfied, wherein trepresents the thickness of the section containing the different surfacematerial. When the thickness is within the above range, the adhesion ofthe particle surface is satisfactory and reflection and scattering canbe prevented from occurring at the interface between the inorganicparticle and the organic component. It is preferable that 10≦t (nm),because the advantage of preventing the reflection and scattering isgreat. It is preferable that t≦150 (nm), because the advantage ofpreventing the reflection and scattering is greater and the inorganicparticles can be prevented from being aggregated; hence, the inorganicparticles can be preferably used. When 40≦t (nm), the inorganicparticles can be more preferably used. This is because the reflectionand scattering of UV rays used for an ordinary photolithographic processcan be effectively prevented. When t≦100 (nm), the inorganic particlescan be more preferably used. When the thickness is within the aboverange, the inorganic particles can be prevented from being aggregatedand the thickness is uniform; hence, the advantage of preventing thereflection and scattering is great. The section containing the differentsurface material preferably has a uniform thickness and is preferablyflat as described above; however, an aspect of the section is notparticularly limited to the above and the section may be irregular orgranular in some cases. A method for joining the inorganic particles tothe section containing the different surface material is notparticularly limited as long as the section is not substantially removedfrom the inorganic particles during the handling (compounding or thelike) of the photosensitive ceramic composite, which is paste. Examplesof the method include a method of using a physical binding effectobtained by plasma-treating the surface of the inorganic particles toroughen the surface and then providing the different surface material onthe resulting surface; a method of allowing a solution, for forming thedifferent surface material, to contain a coupling agent (for example,silane coupling agent SILA-ACE manufactured by Chisso Corporation,vinyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane,3-methacryloxypropyltrimethoxysilane, andN,N′-bis[3-(trimethoxysilyl)propyl]-ethylenediamine) for enhancing thebonding force by chemically modifying the interface; and a method ofenhancing the adhesion using an adhesive (for example, MechanofusionAMS-Lab, a surface modifier manufactured by Hosokawamicron Corporation)based on a mechanochemical reaction caused by the collision ofparticles.

[0034] The ratio (S2/S1) of the area (S2) of the section containing thedifferent surface material to the surface area (S1) of each inorganicparticle is most preferably 1. The section need not entirely cover theinorganic particle. In that case, the ratio S2/S1 is preferably 0.4 ormore (more preferably 0.6 or more and further more preferably 0.8 ormore).

[0035] The following formulas are preferably satisfied:

0.05≦R1−R2

−0.15≦R2−R3

[0036] wherein R1 represents the refractive index of the inner sectionof the inorganic particle, R2 represents the refractive index of thematerial having low refractive index according to the present invention,and R3 represents the refractive index of the photosensitive organiccomponent. Since inorganic materials have a density greater than that oforganic materials in general, the refractive index of the inorganicparticle is greater than that of the photosensitive organic component.Therefore, a difference in refractive index between the differentsurface material and the organic component can be reduced by selecting acondition that the refractive index of the different surface material isless than that of the inorganic particle, whereby the advantage ofpreventing the light reflection and scattering is enhanced. The upperlimit of the refractive index difference (R1−R2) is not particularlylimited and is preferably 1 or less (more preferably 0.6 or less andfurther more preferably 0.4 or less). This is because the refractiveindex of the inorganic particle does not exceed 2.5 in usual, therefractive index of air is 1.0, and the refractive index of thedifferent surface material is equal to an intermediate therebetween. Therefractive index difference (R2−R3) is preferably −0.15 or more asdescribed above because scattering occurs due to a difference inrefractive index when the refractive index R2 of the material having lowrefractive index is extremely less than the refractive index R3 of thephotosensitive organic component. The upper limit of the refractiveindex difference (R2−R3) is preferably 0.8 or less (more preferably 0.5or less and further more preferably 0.3 or less). This is because therefractive index of the organic component hardly exceeds 2.0 and anextremely large difference in refractive index causes scattering.

[0037] When the refractive index of the material having low refractiveindex according to the present invention varies in the thicknessdirection, the refractive index of a surface portion is employed.

[0038] When the refractive index of the material having low refractiveindex cannot be measured, the photosensitive ceramic composite havingthe above configuration according to the present invention can beidentified by the method described below.

[0039] The photosensitive ceramic composite can be identified when theformula 1.1≦ST1/ST2 is satisfied, wherein ST1 represents the rectilinearbeam transmittance of the photosensitive ceramic composite and ST2represents the rectilinear beam transmittance of the photosensitiveceramic composite that does not have the section containing the materialhaving low refractive index.

[0040] The photosensitive ceramic composition having no sectioncontaining the material with low refractive index may have chemicalcomposition different from that of the photosensitive ceramic compositeexcept for the material having low refractive index as long as thephotosensitive ceramic composition has the same optical factors, whichaffect the rectilinear beam transmittance, as those of thephotosensitive ceramic composite. The optical factors are as follows:the refractive index of the inorganic particles, the refractive index ofthe photosensitive organic component, and the volume ratio of theinorganic particles to the photosensitive organic component, and theaverage particle size and sphericity of the inorganic particles.

[0041] The rectilinear beam transmittance is defined as the percentageof the amount of light propagated in parallel without changing the pathin the amount of light applied to a sample. Light beams used for themeasurement preferably have the same wavelength as that of light beamsused for exposure and include a g-beam having a wavelength of 436 nm andan i-beam having a wavelength of 365 nm. Examples of a light source ofsuch beams include a high-pressure mercury lamp and a light source (suchas a halogen lamp for emitting visible rays) for emitting beams havingthe same wavelengths as those of the g- and i-beams. In an embodiment ofthe present invention, the value of the rectilinear beam transmittanceratio (ST1/ST2) is preferably 1.2 or more and more preferably 1.5 ormore.

[0042] The material having low refractive index according to the presentinvention preferably contains at least one selected from the groupconsisting of ZnS, CeF₂, MgF₂, and SiO₂. This is because those compoundshave a relatively small absorption coefficient and are thereforeextremely transparent. The absorption coefficient varies depending on amethod for forming a layer. According to data disclosed in S. Aizenburgand R. Chabot, J. Appl. Phys. 42 (1971) 2953; Pei-Fu Gu, Yen Ming Chan,Xue Qun Hu, and Jin-Fa Tang, Appl. Opt. 28 (1989) 3318; and the like,the absorption coefficient of SiO₂ is about 2×10 ⁻⁵. The data wasdetermined using a light beam having a wavelength of 550 nm. Accordingto the above documents, the absorption coefficient can be determinedwith respect to a desired wavelength, that is, the wavelength of a lightbeam used for measuring the beam transmittance, by calculation.

[0043] The average particle size of the inorganic particles ispreferably within a range of 0.1 to 10 μm. The particle size isdetermined using a laser-scattering particle size distribution meter.The average particle size is equal to a 50%-distribution particle size.The 50%-distribution particle size is defined as the particle size ofwhich the distribution is 50%, and the average particle size hereinaftermeans the 50%-distribution particle size unless otherwise specified.When the average particle size is less than 0.1 μm, the inorganicparticles cannot be mixed with the photosensitive organic component welland cannot therefore be dispersed therein and the inorganic particleshave a surface area insufficient to provide the section containing thedifferent surface material. In contrast, when the average particle sizeis more than 10 μm, principle light in the ultraviolet to visible rangeis scattered. The average particle size is more preferably 0.3 μm ormore. This is because the inorganic particles can be readily mixed withthe photosensitive organic component and dispersed therein by a physicalmethod using a three-roll mill. Furthermore, the average particle sizeis preferably 5 μm or less. When the average particle size is 5 μm orless, the particles hardly scatter light and a mixture of thephotosensitive organic component and the particles has a constantviscosity, whereby a difference in the strength of each sheet preparedusing the mixture can be reduced.

[0044] Furthermore, the average particle size is preferably 0.5 μm ormore. When the average particle size is 0.5 μm or more, the particlesdispersed in the photosensitive organic component efficiently absorblight for exposure and a developing solution uniformly penetrate theparticles when the particles are immersed in the solution in adeveloping step, whereby the time of an exposing step and the time ofthe developing step can be reduced.

[0045] Furthermore, the average particle size is preferably 3.5 μm orless when a high-resolution pattern is necessary, because across-sectional shape formed by exposure and development is flat.

[0046] The formula N1−N2<0.15 is preferably satisfied, wherein N1represents the refractive index of a component having a maximalrefractive index and N2 represents the refractive index of a componenthaving a minimal refractive index. The maximal refractive indexcomponent is defined as a component having the largest refractive indexamong components which are contained in the composite and of which therefractive index can be individually determined. The minimal refractiveindex component is defined as a component having the smallest refractiveindex among components which are contained in the composite and of whichthe refractive index can be individually determined. When the aboveformula is satisfied, light scattering can be readily reduced.

[0047] The inorganic particles preferably contain at least one selectedfrom the group consisting of alumina, zirconia, magnesia, beryllia,mullite, spinel, forsterite, anorthite, celsian, and aluminum nitride.Those compounds are contained in glass ceramics for the purpose ofenhancing the mechanical strength, controlling the thermal propertiessuch as the thermal expansion coefficient, or controlling the dielectricconstant or the dielectric loss tangent. The compounds have a smallthermal expansion coefficient, which is within an order of magnitude of10⁻⁶ to 10⁻⁷ (/° C.) when measured at 25° C. to 300° C. Therefore, theheat distortion of the compounds is slight. Thus, the section containingthe different surface material is hardly removed from each inorganicparticle even if the temperature varies depending on manufacturing stepsafter the section is formed on the inorganic particle.

[0048] The inorganic particles are sintered in a firing step. In orderto prepare a substrate according to the present invention, the firingtemperature is preferably 1000°0 C. or less and more preferably 600°0 C.to 950° C., that is, the inorganic particles are preferably fired at lowtemperature. Since basic properties of the substrate depend onproperties of the inorganic particles, the inorganic particles must becarefully selected. The basic properties include electricalcharacteristics, the strength, and the thermal expansion coefficient.The following material is selected: a ceramic material or a glassceramic material that can be fired at low temperature. In the glassceramic material, a glass component is sintered and a ceramic componentfunctions as a filler. Therefore, the substrate prepared using theinorganic particles has a desired strength and dielectriccharacteristics.

[0049] Most of known glass ceramic materials have high dielectric lossand high-frequency characteristics thereof are therefore insufficient.The inorganic particles of the present invention can be preferably firedat 600° C. to 950° C., whereby a substrate including wires containingCu, Ag, or Au is prepared. The substrate has a thermal expansioncoefficient close to that of a printed circuit board or a chip componentcontaining GaAs or the like and also has low dielectric constant anddielectric loss at high frequencies.

[0050] Components of the inorganic particles are selected depending onthe properties described above and examples of the components includethe four examples below.

[0051] A first example is a system containing an aluminosilicatecompound represented by the formula RxO—Al₂O₃—SiO₂, wherein R representsan alkaline metal element or an alkaline earth metal element and x isequal to 2 or 1 when R represents such an alkaline metal element oralkaline earth metal element, respectively. Examples of thealuminosilicate compound, which is not particularly limited, includeanorthite (CaO—Al₂O₃—2SiO₂) and celsian (BaO—Al₂O₃—SiO₂), which areinorganic compounds used for manufacturing low-temperature sinteredceramics.

[0052] A second example is a mixture containing 50% to 90% of glassparticles and 10% to 50% of quartz particles and/or amorphous silicaparticles on a weight basis. The glass particles contain borosilicateglass. It is preferable that the quartz particles and/or the amorphoussilica power be not melted together with borosilicate glass orcordierite. The quartz particles and/or the amorphous silica particlespreferably contain spherical silica particles because the filling factorof slurry is high. Quartz and amorphous silica individually have anextremely small dielectric loss tangent within an order of magnitude of10⁻⁵ and therefore have a small dielectric loss. Therefore, the quartzparticles and/or the amorphous silica power contained in the inorganicparticles reduce the dielectric loss of the particles.

[0053] A third example is a mixture containing 30% to 60% ofborosilicate glass particles, 20% to 60% of quartz particles and/oramorphous silica particles, and 20% to 60% of ceramic particlescontaining at least one selected from the group consisting ofcordierite, spinel, forsterite, anorthite, and celsian on a weightbasis.

[0054] A fourth example is a mixture containing 30% to 60% of glassparticles and 40% to 70% of ceramic particles. The glass particlescontain 85% or more of oxides and have a SiO₂ content of 30% to 70%, anAl₂O₃ content of 5% to 40%, a CaO content of 3% to 25%, and a B₂O₃content of 3% to 50% on a weight basis. The ceramic particles contain atleast one selected from the group consisting of alumina, zirconia,magnesia, beryllia, mullite, spinel, forsterite, anorthite, celsian, andaluminum nitride. Those percentages are expressed on a weight basis.

[0055] The inorganic particles can contain a filler, which is usuallythe ceramic particles as described above. The filler is useful inenhancing the mechanical strength of the substrate and useful inadjusting the thermal expansion coefficient thereof. In particular,alumina, zirconia, mullite, and anorthite are satisfactory in suchfunctions. When the inorganic particles are a mixture of those ceramicparticles, the inorganic particles can be fired at 800° C. to 900° C.,whereby the substrate is allowed to have a desired strength, dielectricconstant, thermal expansion coefficient, sintered density, volumeresistivity, and shrinkage.

[0056] The total content of SiO₂, Al₂O₃, CaO, and B₂O₃ in the glassparticles is preferably 85% by weight or more. The content of theremainder is 15% by weight or less, the remainder being Na₂O, K₂O, BaO,PbO, Fe₂O₃, Mn oxides, Cr oxides, NiO, and/or Co oxides. The ceramicparticles, mixed with the glass particles having a content of 30% to 60%by weight, having a content of 40% to 70% by weight function as thefiller. The content of SiO₂ in the glass particles is preferably 30% to70% by weight. When the SiO₂ content is less than 30% by weight, thestrength and stability of a glass layer are too low and the dielectricconstant and thermal expansion coefficient of the substrate are toohigh; hence, values of those characteristics are apt to be outsidedesired ranges. When the SiO₂ content is more than 70% by weight, thesubstrate obtained by firing has an extremely large thermal expansioncoefficient and the inorganic particles cannot be fired at 1000° C. orless. The Al₂O₃ content is preferably 5% to 40% by weight. When theAl₂O₃ content is less than 5% by weight, the strength of the glass layeris low and the inorganic particles cannot be fired at 1000° C. or less.When the Al₂O₃ content is more than 40% by weight, the temperature ofallowing the glass particles to be fritted is extremely high. The CaOcontent is preferably 3% to 25% by weight. When the CaO content is lessthan 3% by weight, the substrate do not have a desired thermal expansioncoefficient and the inorganic particles cannot be fired at 1000° C. orless. When the CaO content is more than 25% by weight, the dielectricconstant and thermal expansion coefficient of the substrate areextremely high. Since B₂O₃ allows glass frit to be melted at about 1300°C. to 1450° C., the B₂O₃ content is preferably adjusted such that theinorganic particles can be fired at 800° C. to 900° C. even if the Al₂O₃content is high, whereby electrical, mechanical, and thermalcharacteristics of the substrate are not deteriorated. Suchcharacteristics include the dielectric constant, the strength, thethermal expansion coefficient, and the sintering temperature. Thus, theB₂O₃ content is preferably 3% to 50% by weight.

[0057] When the inorganic particles are a mixture of a plurality oftypes of particles, the section containing the different surfacematerial according to the present invention need not be placed on thesurface of each particle, contained in the mixture, having a refractiveindex less than that of the organic component in some cases. The sectioncontaining the different surface material according to the presentinvention is preferably placed on the surface of each inorganic particlewhen the inorganic particles has a refractive index of 1.6 or more (morepreferably 1.65 or more and further more preferably 1.7 or more) and thecontent of the high-refractive index material in the inorganic particlesis 5% or more (more preferably 10% or more and further more preferably20% or more) on a weight basis, whereas the refractive index and thecontent are not particularly limited.

[0058] In order to use the inorganic particles to prepare green sheets,the content of the inorganic particles in the photosensitive ceramiccomposite is preferably 60% to 95% (more preferably 60% to 90% andfurther more preferably 65% to 85%) on a weight basis when thephotosensitive ceramic composite does not contain an organic solvent.When the inorganic particle content is less than the lower limit of theabove range, spaces between the inorganic particles are filled with theorganic component, whereby ventilation is impaired, the organiccomponent cannot be readily removed in the sintering step, and thedimensional stability of the green sheets is impaired because the volumeof the green sheets varies depending on the amount of the organiccomponent removed in the sintering step. In contrast, when the inorganicparticle content is more than the upper limit, the flexibility of thegreen sheets is impaired.

[0059] In the present invention, the photosensitive organic component,which is essential for the photosensitive ceramic composite, preferablycontains an acrylic copolymer with side chains having a carboxyl group,a photoreactive compound, and a photo-polymerization initiator. Thephotosensitive organic component may further contain an additive such asa binder polymer, an enhancer, an ultraviolet absorbent, a dispersingagent, a surfactant, an organic dye, a plasticizer, a thickening agent,an oxidation inhibitor, or an antigelling agent according to needs.

[0060] The inorganic particles and the photosensitive organic componentare essential for the photosensitive ceramic composite of the presentinvention. The photosensitive organic component preferably contains a(meth)acrylate compound (sub-component A1) and a urethane compound(sub-component A2) having an ethylenic unsaturated group. The term“(meth)acrylate” means acrylate and/or methacrylate, and the sameapplies to the description below, for example, the term “(meth)acryloyl”means acryloyl and/or methacryloyl.

[0061] In the present invention, the photosensitive organic componentmeans an integrated whole that includes organic compounds in thephotosensitive ceramic composite, that is, the photosensitive organiccomponent means the remainder of the photosensitive ceramic compositeapart from inorganic compounds. The photosensitive ceramic composite ofthe present invention is in a paste state when used in an applying stepor a stacking step and is preferably dispersed in a solvent. In thebelow description about parameters (for example, the content of each ofsub-components A1, A2, and B) associated with the composition of thephotosensitive ceramic composite, the amount of the solvent is omitted.

[0062] In the present invention, the (meth)acrylate compound(sub-component A1) contained in the photosensitive organic componentallows a reaction initiated by light to occur, that is, the(meth)acrylate compound allows a crosslinking reaction or apolymerization reaction to occur, and therefore plays an important rolein forming a pattern. Thus, the (meth)acrylate compound must have one ormore (meth)acrylate groups functioning as photopolymerizable unsaturatedgroups.

[0063] In the present invention, R1 represents hydrogen or a methylgroup and preferably hydrogen.

[0064] At least one group represented by R2 preferably has an ethyleneoxide group because of the compatibility. Those may be used alone or incombination. The refractive index of the photosensitive organiccomponent (component A) can be readily controlled depending on that ofsub-component A1 functioning as a photosensitive monomer. The refractiveindex of sub-component A1 is preferably 1.5 to 1.7. The content ofsub-component A1 in the photosensitive organic component is preferably10% to 80% (more preferably 10% to 60% and further more preferably 15%to 40%) on a weight basis.

[0065] In formula (1), an organic group represented by R3 is preferablyan aromatic group such as phenyl group, a phenol group, a biphenylgroup, a para-cumylphenol group, a nonylphenol group, a bisphenol Agroup, or a bisphenol F group because the refractive index is high.

[0066] Preferable examples of the compound represented by formula (1)include bifunctional (meth)acrylates such as bisphenol Adi(meth)acrylate, di(meth)acrylate of a bisphenol A-ethylene oxideadduct, di(meth)acrylate of a bisphenol A-propylene oxide adduct,bisphenol F di(meth)acrylate, di(meth)acrylate of a bisphenol F-ethyleneoxide adduct, and di(meth)acrylate of a bisphenol F-propylene oxideadduct; and monofunctional (meth)acrylates such as phenoxyethyl(meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenyl(meth)acrylate, phenoxydiethylene glycol (meth)acrylate,phenoxypolyethylene glycol (meth)acrylate, phenol (meth)acrylatemodified with ethylene oxide, para-cumylphenol (meth)acrylate modifiedwith ethylene oxide, nonylphenol (meth)acrylate modified with ethyleneoxide, and nonylphenol (meth)acrylate modified with propylene oxide,because the refractive index is high. Para-cumylphenol (meth)acrylatemodified with ethylene oxide is particularly preferable.

[0067] In the present invention, R0 represents a group represented bythe formula CH2═CR1COO—(R2)n-, a hydrogen atom, or a halogen atom andthe hydrogen atom is preferable. When R0 represents the group (whenformula (1) has two pairs of R1 or R2), triples of R1, R2, and n informula (1) may be different from each other or the same as each other,respectively, for at least one pair.

[0068] Sub-component A1, represented by formula (1), contained in thecomposite of the present invention may be a single compound or a mixtureconsisting of two or more different compounds.

[0069] Sub-component A1can be prepared by the method described below;however, the present invention is not limited the method. Sub-componentA1is prepared by esterifying monohydroxy or dihydroxy alcohol with(meth)acrylic acid according to an ordinary procedure to producemono(meth)acrylate or di(meth)acrylate, wherein the alcohol has analkylene oxide unit, formed by an addition reaction, represented by theformula HO—(R2)n-R3 or (HO—(R2)n)2R3 and the (meth)acrylic acid isrepresented by the formula CH2═CR1COOH. In the esterification, the(meth)acrylic acid may be converted into a highly reactive compound,such as acid halide, which is then subjected to the reaction, and abyproduct-removing agent (such as a dehydrating agent or a hydrogenhalide-removing agent) and/or a catalyst may be used.

[0070] In the present invention, the urethane compound (sub-componentA2) having an ethylenic unsaturated group is not particularly limitedbut is defined as a compound having a urethane bond (—NHCOO—). Examplesof an organic group in the urethane compound include a vinyl group, anallyl group, an acryloyl group, a mathacryloyl group, an alkylene group,an alkylene oxide group, an alkyl group, an aryl group, an arylenegroup, an aralkyl group, an aralkylene group, a hydroxyalkyl group, anda hydroxyalkylene group, other than the urethane bond. Among thosegroups, the alkylene oxide group is preferable in view of thecompatibility. The urethane compound may have a linear, branched, orcyclic molecular structure, which may have a linear, branched, and/orcyclic portion. The molecular structure is not particularly limited andis preferably linear. The urethane compound preferably has a molecularweight of 800 to 100000 (more preferably 10000 to 50000 and further morepreferably 15000 to 45000). When the molecular weight is less than thelower limit of the above range, the urethane compound is excessivelyrigid, which is not preferable. When the molecular weight is more thanthe upper limit of the range, the urethane compound has excessively highviscosity, which is not preferable. The amount of the urethane bond inthe urethane compound is preferably 0.000016 to 0.0125 mol/g, morepreferably 0.00002 to 0.001 mol/g, and further 0.000022 to 0.0007 mol/g.The urethane bond amount is less than the lower limit of the aboverange, the urethane compound has low flexibility, which is notpreferable. When the amount is more than the upper limit of the range,the urethane compound has excessively high elastic modulus, which is notpreferable.

[0071] In the present invention, the ethylenic unsaturated group of theurethane compound (sub-component A2) preferably has low steric hindranceand a high degree of freedom in molecular motion in view of thecrosslinking reaction, that is, it is not preferable that the ethylenicunsaturated group have a large number of large substituents. Therefore,the ethylenic unsaturated group preferably has a single substituentprimarily and preferably has two substituents secondarily. Thecrosslinking reaction is promoted depending on chemical properties ofsuch a substituent or substituents in some cases. Examples of theethylenic unsaturated group include a vinyl group, an allyl group, anacryloyl group, and a mathacryloyl group. In particular, the acryloylgroup and the mathacryloyl group are preferable; however, the ethylenicunsaturated group is not limited to those groups.

[0072] In order to allow a polymer to have such side chains, groupshaving active hydrogen in the polymer are allowed to react with acryloylchloride, methacryloyl chloride, allyl chloride, or an ethylenicunsaturated compound having a glycidyl group or an isocyanate group.Examples of the ethylenic unsaturated compound having the glycidyl groupinclude glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether,glycidyl crotonate, and glycidyl isocrotonate. Examples of the ethylenicunsaturated compound having the isocyanate group include (meth)acryloylisocyanate and (meth)acryloyl ethylisocyanate. One mole of the groupshaving active hydrogen in the polymer are preferably allowed to reactwith 0.05 to 0.95 mole of acryloyl chloride, methacryloyl chloride,allyl chloride, or the ethylenic unsaturated compound having theglycidyl group or the isocyanate group. When the groups having activehydrogen are mercaptan groups, amino groups, or hydroxy groups, all ofthe groups having active hydrogen may be allowed to react with thosecompounds for forming the side chains. However, when the groups havingactive hydrogen are carboxyl groups, the groups having active hydrogenare preferably allowed to react with those compounds such that thepolymer has a desired acid value.

[0073] In the urethane compound of the present invention, the number ofthe ethylenic unsaturated group is preferably one to six per molecule,more preferably one to four, and further more preferably two to three.Alternatively, the amount of the ethylenic unsaturated group in theurethane compound is preferably 0.000016 to 0.0075 mol/g, morepreferably 0.000016 to 0.005 mol/g, and further more preferably 0.000033to 0.0038 mol/g. When the number or amount of the ethylenic unsaturatedgroup is less than the lower limit of the number or amount range,respectively, the polymer cannot be sufficiently cured, which is notpreferable. When the number or amount of the ethylenic unsaturated groupis more than the upper limit of the number or amount range,respectively, the polymer seriously shrinks when cured, which is notpreferable.

[0074] When the urethane compound is allowed to function as aphotoreactive component, physical properties of the sheets treated in aphoto-curing step can be maintained such that the properties are fit forsubsequent steps. Furthermore, stress applied to the sheets can bereduced in the firing step, whereby defects can be prevented fromoccurring in the firing step.

[0075] The urethane compound having the ethylenic unsaturated group ispreferably a compound, represented by formula (2), having an ethyleneoxide group:

CH2═CX1COO—X2—(X3—X4)n-X3—X2—OCOCX1═CH2  (2)

[0076] wherein X1 represents hydrogen, a hydroxy group, or a methylgroup; X2 and X4 each represent an alkylene oxide group or an alkyleneoxide oligomer group; at least one of the group represented by X2 andthe group represented by X4 has an ethylene oxide group; X3 representsan aliphatic diisocyanate residue or a cycloaliphatic diisocyanateresidue having a urethane bond; and n represents an integer of 1 to 10.

[0077] In order to enhance the compatibility, at least one of thealkylene oxide group and the oligomer group represented by X2 or X4 informula (2) preferably has the ethylene oxide group. In particular, thegroup represented by X4 preferably has an oligomer segment having anethylene oxide unit and a propylene oxide unit. In the presentinvention, sub-component A1 functioning as a photosensitive monomer ispreferably monofunctional or bifunctional (meth)acrylate having anaromatic ring. Sub-component A1 is less compatible with a polymer(sub-component A3) with side chains having a carboxyl group becausesub-components A1 and A3 have different polarities. However, when theurethane compound with the ethylenic unsaturated group has the ethyleneoxide group with high polarity, the urethane compound has a portion witha polarity close to that of the polymer (sub-component A3) and anotherportion with a polarity close to that of the photosensitive monomer;hence, the urethane compound is compatible with both the polymer(sub-component A3) and sub-component A1, which is the photosensitivemonomer. The content of the ethylene oxide unit in the oligomer ispreferably within a range of 8% to 70% by weight. When the content ofthe ethylene oxide unit is more than 70% by weight, the photo-curedoligomer has high elastic modulus, which causes an increase in stressapplied to the substrate to cause an increase in defects such asbreakages of the substrate. Therefore, the content more than 70% is notpreferable. When the content is less than 8%, the photosensitive organiccomponent is less compatible with other components and the haze istherefore high, whereby a pattern cannot be precisely formed. Therefore,the content less than 8% is not preferable.

[0078] The haze of the photosensitive organic component can bedetermined according to the following procedure: the photosensitiveorganic component is applied to a glass substrate, which is thenmeasured with a haze meter. A layer, placed on the substrate, containingthe photosensitive organic component has a thickness of 100 μm. The hazeis preferably 0.5 or less.

[0079] The group represented by X4 in formula (2) preferably has a totalmolecular weight of 800 to 10000, the total molecular weight beingobtained by multiplying the formula weight of the group, represented byX4, by n. When the total molecular weight is 800 or more, the urethanecompound is flexible. When the total molecular weight is 10000 or less,the urethane compound can be readily handled.

[0080] The organic group, represented by X3, having the urethane bond ispreferably formed by the condensation of a diisocyanate group and ahydroxyl group. Examples of a compound having the diisocyanate groupused herein include an aliphatic diisocyanate compound such as1,4-diisocyanatebutane and 1,6-diisocyanatehexan, an aromaticdiisocyanate compound such as 1,4-phenylenediisocyanate andtolylenediisocyanate, and a cycloaliphatic diisocyanate compound such asisophoronediisocyanate. In particular, isophoronediisocyanate ispreferable; however, the compound having the diisocyanate group is notlimited thereto.

[0081] Examples of the urethane compound, used herein, having theethylenic unsaturated group include UA-2235PE (a molecular weight of14000 and an ethylene oxide (EO) content of 20%), UA-3238PE (a molecularweight of 19000 and an EO content of 10%), UA-3348PE (a molecular weightof 22000 and an EO content of 15%), UA-5348PE (a molecular weight of39000 and an EO content of 23%), TN-1 (a molecular weight of 1000), TN-5(a molecular weight of 2000), UV-6100B (a molecular weight of 6500), andUV-7000B (a molecular weight of 3500). UA-2235PE, UA-3238PE, UA-3348PE,and UA-5348PE are available from Shin-Nakamura Chemical Co., Ltd.; TN-1and TN-5 are available from Negami Chemical Industrial Co., Ltd.; andUV-6100B and UV-7000B are available from The Nippon Synthetic ChemicalIndustry Co., Ltd.

[0082] The photosensitive organic component (component A) used hereinpreferably contains the polymer (sub-component A3) with the side chainshaving the carboxyl group because the photosensitive organic componentcan be developed with an alkaline solution. The polymer (sub-componentA3) with the side chains having the carboxyl group can be obtained bypolymerizing or copolymerizing a carboxyl group-containing monomer suchas acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleicacid, fumaric acid, vinyl acetate, or an acid anhydride derived from anyone of those compounds; and/or a monomer such as methacrylic ester,acrylic ester, styrene, acrylonitrile, vinyl acetate, 2-hydroxyethylacrylate using a radical polymerization initiator. A monomer forpreparing the polymer is not limited to those monomers.

[0083] The polymer (sub-component A3) with the side chains having thecarboxyl group preferably has an acid value of 50 to 140. When the acidvalue is 140 or less, the photosensitive organic component can bereadily developed. When acid value is 50 or more, a fine pattern can beobtained because unexposed regions are soluble in a developing solution,which need not therefore have high concentration, and such a solutiondoes not cause damage in exposed regions. Preferable examples of thepolymer (sub-component A3) with the side chains having the carboxylgroup a copolymer prepared by copolymerizing (meth)acrylic ester and(meth)acrylic acid because such a copolymer is thermally decomposed atlow temperature when fired.

[0084] In common with the urethane compound having the ethylenicunsaturated group, the polymer (sub-component A3) with the side chainshaving the carboxyl group preferably has side chains having an ethylenicunsaturated group because a pattern can be readily formed. Aconfiguration of the polymer (sub-component A3) having the side chainshaving the ethylenic unsaturated group is substantially the same as thatof the urethane compound having the ethylenic unsaturated group.

[0085] The content of the polymer (sub-component A3) in thephotosensitive organic component is preferably 10% to 80% by weight.When the polymer content is less than the lower limit of the aboverange, the degree of photo-curing is insufficient. When the polymercontent is more than the upper limit of the range, the degree ofphoto-curing is excessively high. The polymer content outside the rangeis not preferable.

[0086] The polymer (sub-component A3) with the side chains having thecarboxyl group and the urethane compound (sub-component A2) having theethylenic unsaturated group, which are contained in the photosensitiveorganic component, are inferior in absorbing the energy of light raysused for activation in general. Therefore, in order to initiate aphotoreaction, the photosensitive organic component preferably containsa photo-polymerization initiator. The photosensitive organic componentmay further contain an enhancer for assisting the photo-polymerizationinitiator in some cases. Examples of the photo-polymerization initiatorinclude an initiator in which a single molecule is directly cleaved, aninitiator in which electrons transferred between ion pairs, a hydrogentransfer initiator, and a bimolecular initiator. Thephoto-polymerization initiator used herein preferably produces activeradicals. One or more species of photo-polymerization initiator and/orenhancer may be used. The content of the photo-polymerization initiatorin the photosensitive organic component is preferably 0.05% to 10% andmore preferably 0.1% to 10% on a weight basis. When the initiatorcontent is within the above range, the residue of exposed regions iswithin a desired range and the sensitivity is satisfactory.

[0087] The content of the photosensitive organic component in thephotosensitive ceramic composite is preferably 10% to 40% by weightwhile the photosensitive organic component contains the organic solvent.When the photosensitive organic component is formed into coatings orgreen sheets, the flexibility and ventilation thereof must be satisfied.The component of the photosensitive organic component affects thosecharacteristics. In order to enhance the flexibility, the component ofthe photosensitive organic component is preferably high; however, spacesbetween the inorganic particles are filled with the photosensitiveorganic component and the ventilation is impaired when the content isexcessively high. Thus, the component of the photosensitive organiccomponent is more preferably 20% to 35% by weight.

[0088] The photosensitive ceramic composite of the present invention canbe prepared according to the procedure below.

[0089] The sections containing the material having low refractive indexare each formed on the corresponding inorganic particles.

[0090] In order to form each section, containing the material having lowrefractive index, on at least one area of the surface of each inorganicparticle, the following method is preferably used: a method for formingthe section on the inorganic particle surface in a gas atmosphere or avacuum atmosphere by a spray coating process or a vacuum vapordeposition process or a method for forming the sections by applying asolution in which a compound or precursor forming the sections isdissolved or dispersed onto the inorganic particles and then evaporatinga solvent of the solution or applying light or heat to the resultinginorganic particles to allow a chemical reaction in the solution on theinorganic particles.

[0091] In a process using a spray dryer, a liquid containing thematerial having low refractive index is sprayed from nozzles on theinorganic particles placed on a hot plate or placed in a hot air streamand the liquid placed on the particle surface is then instantaneouslydried.

[0092] In the vacuum vapor deposition process, a metal or nonmetal pieceis subjected to evaporation in a high vacuum atmosphere by heating andvapor evaporated from the piece, which is an evaporation source, isallowed to adhere to the inorganic particles, which are evaporationtargets. Since the evaporation is performed under vacuum conditions, thedegree of vacuum is preferably maintained high such that the distancebetween a heater and the evaporation targets is sufficiently smallerthan the mean free path of evaporated molecules and absorbed moisture ispreferably removed completely by cleaning surfaces. On the other hand,in order to deposit an oxide or nitride on the inorganic particles, asmall amount of an oxygen or nitrogen gas is introduced into theatmosphere, an evaporated or vaporized substance is allowed to reactwith oxygen or nitrogen, and the product is deposited on the inorganicparticles.

[0093] In a process for preparing a solution to allowing the solution toadhere to the inorganic particle surface, the amount of the solutionadhering to the inorganic particle surface can be controlled by varyingthe composition or concentration of the solution and a large amount ofthe inorganic particles can be surface-treated by mixing the inorganicparticles with the solution. When a low-refractive index materialcontaining SiO₂ is formed, the solution is preferably prepared bydissolving a large amount of alkali silicate, obtained by meltingsilicon dioxide and alkali, in water, the solution being referred to aswater glass. Alternatively, the solution is preferably prepared bydispersing inorganic powder, synthesized physically or chemically inadvance, in a dispersion medium such as water or an organic solvent. Inorder to enhance the adhesion of the solution to the inorganicparticles, the solution may contain 0.01% to 3.0% by weight of a silanecoupling agent.

[0094] There are various processes as described above. The easiest oneis a process of preparing a solution containing a low-refractive indexcompound and then mixing the solution with the inorganic particles toallowing the solution adhere to the inorganic particles. The mixture isthen filtrated by aspiration, and the resulting inorganic particles aredried in an oven.

[0095] An organic vehicle is then prepared by mixing the photosensitiveorganic component (for example, the polymer with the side chains havingthe carboxyl group, the photo-polymerization initiator, and the like)with a solvent and/or an additive according to needs and then filtratingthe mixture. The inorganic particles pretreated according to needs andan inorganic compound functioning as a filler are mixed with the organicvehicle using a kneader such as a ball mill such that the inorganicparticles and the inorganic compound are uniformly dispersed in theorganic vehicle, whereby the photosensitive ceramic composite, which isslurry or paste, is prepared. The viscosity of the slurry or paste isadjusted by varying the blending ratio of the inorganic particles to theorganic component, the amount of the organic solvent, and/or the contentof an additive such as a plasticizer according to needs and ispreferably within a range of 1 to 5 Pa·s. The solvent for preparing theslurry or paste is not particularly limited and any solvent having anability to dissolve the photosensitive organic component may be used.Examples of the solvent include methyl cellosolve, ethyl cellosolve,butyl cellosolve, methyl ethyl ketone, dioxane, acetone, cyclohexanone,cyclopentanone, isobutyl alcohol, isopropyl alcohol, tetrahydrofuran,dimethyl sulfoxide, γ-butyrolactone, toluene, trichloroethylene, methylisobutyl ketone, and isophorone. Those compounds may be used alone or incombination.

[0096] The obtained paste is applied onto a film, for example, apolyester film, by an ordinary process such as a doctor blade process oran extrusion-molding process, whereby layers having a thickness of 0.05to 0.5 mm are formed. The solvent is removed from the layers, wherebygreen sheets containing the photosensitive ceramic composite areprepared. Via-holes are formed according to the following procedure: thegreen sheets are subjected to pattern exposure using a photomask havinga pattern for forming the via-holes and the resulting green sheets aredeveloped with an alkali solution.

[0097] In the present invention, since the photosensitive organiccomponent contained in the photosensitive ceramic composite contains thepolymer (sub-component A3) with the side chains having the carboxylgroup, the photosensitive organic component can be developed with analkali solution. Examples of the alkali solution include a metal alkalisolution containing sodium or potassium and an organic alkali solution.In particular, the following solution is preferable: a solutioncontaining a weakly basic metal alkali compound such as sodium carbonate(Na₂CO₃) or potassium carbonate (K₂CO₃) or a solution containing anorganic amine compound having no hydroxy group but one to six carbonatoms, the organic amine compound being at least one selected from thegroup consisting of n-propylamine, t-butylamine, and diisopropylamine.This is because a change in the size of the green sheets can becontrolled within a range of 1 to 1.5 (more preferably 1 to 1.3 andfurther more preferably 1 to 1.2). The concentration of the alkalisolution is usually 0.1% to 3% and more preferably 0.5% to 1.5% on aweight basis. When the concentration is extremely low, soluble portionsof the green sheets cannot be completely removed. When the concentrationis extremely high, a pattern formed by exposure is removed and/or erodedin some cases. The temperature of the development is preferably 20° C.to 50° C. in view of the process management. Examples of a developingprocess include ordinary processes such as an immersing process and aspraying process. The developing time can be reduced and unevenness indevelopment can be prevented by the use of ultrasonic waves.

[0098] A method for manufacturing a substrate using the photosensitiveceramic composite containing the inorganic particles and thephotosensitive organic component includes the following steps:

[0099] (1) a step of forming the photosensitive ceramic composite intophotosensitive green sheets;

[0100] (2) a step of trimming the resulting photosensitive green sheetsby a photolithographic process;

[0101] (3) a step of stacking the resulting photosensitive green sheets;and

[0102] (4) a step of firing the resulting photosensitive green sheets.

[0103] In the above method, the term “a step of trimming the resultingphotosensitive green sheets by a photolithographic process” is definedas a step of shaping an outside region of the photosensitive ceramiccomposite formed into the sheets or a step of shaping the outlines(including inside end regions) of the green sheets functioning asdielectric layers, wherein the outlines do not include those of poressuch as perforations used for forming contact holes such as via-holes.

[0104] As a matter of course, the outside region is defined as a sideface of the substrate (or an electronic circuit) that can be observed inthe direction perpendicular to a normal line of the substrate.Furthermore, a principal face of the substrate is defined as an upperface thereof when the substrate is assumed to be substantially a flatsheet. Alternatively, the principal face is defined as a face having anormal line extending in the direction that a maximum value is obtainedwhen sizes of lines normal to outer faces of the substrate are summedup, wherein the normal lines are assumed to have a size that is inproportion to the area of each outer face. The outlines except for thoseof such pores correspond to those of holes larger than the via-holes(the maximum diameter is 300 μm) and include openings, perforatedstructures, and structures similar to a patio.

[0105] In the above configuration, the photosensitive green sheetstrimmed by the photolithographic process each have a processed regionand the area of the processed region is substantially the same as thatof a circle having a diameter of 1 to 50 mm preferably (more preferably5 to 40 mm and further more preferably 10 to 30 mm). The diameter isless than the lower limit of the above range, the reproducibility of thecross-sectional shape is lowered, that is, the processing accuracy islowered. In contrast, when the diameter is more than the upper limit ofthe above range, stress is concentrated on irregularities formed in thetrimming step, whereby warpage occurs in the firing step. Therefore, thediameter outside the above range is not preferable. On the other hand,for the shape of the photosensitive green sheets trimmed by thephotolithographic process, the following formula is preferablysatisfied:

3 mm≦L≦200 mm

[0106] wherein L represents the sum of the outside perimeter and insideperimeter of each sheet trimmed by the photolithographic process and thelength of a portion common to an outside region and an inside region ofthe sheet is excluded from the sum. The sum L is more preferably 12 to100 mm.

[0107] In order to prepare a substrate including isolated portions incross section parallel to a principal face of the substrate (or anelectronic circuit), the trimming step using the photolithographicprocess may include the sub-steps below.

[0108] (1) First, the photosensitive green sheets are arranged on acarrier film.

[0109] (2) Secondly, the photosensitive green sheets on the carrier filmare trimmed by the photolithographic process, and the resultingphotosensitive green sheets are processed such that the sheets eachinclude portions isolated each other as described above. The processingis performed such that the arrangement of the isolated portions on thecarrier sheet corresponds to that in the completed substrate.

[0110] (3) Thirdly, the sheets including the isolated portions obtainedby the photolithographic process are transferred from the carrier filmwhile the arrangement the isolated portions is maintained, and theresulting sheets are stacked.

[0111] (4) Finally, the stacked ceramic green sheets are fired.

[0112] According to the above procedure, the substrate having thebranched structure can be readily prepared. This is because thephotosensitive green sheets isolated each other can be arranged on thesingle carrier film while the arrangement of the isolated portions ismaintained. In contrast, in a punching process using a die, since thephotosensitive green sheets are punched together with the carrier film,a plurality of the trimmed sheets must be individually aligned with thedie. In the present invention, since the photosensitive green sheets canbe formed on the single carrier film and the resulting sheets can bestacked, the photosensitive green sheets can be precisely aligned witheach other readily when stacked.

[0113] In the present invention, the term “a step of stacking thephotosensitive green sheets trimmed by the photolithographic process” isdefined as a step of stacking at least one or more trimmedphotosensitive green sheets or non-photosensitive green sheetscontaining the inorganic particles and a non-photosensitive organiccomponent. Since the photolithographic process has limitations on thedepth, thin sheets are processed by the photolithographic process andthen stacked, whereby a substrate having a desired thickness can beobtained. The photosensitive green sheets preferably have a thickness of10 to 500 μm (more preferably 25 to 400 μm and further more preferably50 to 300 μm). When the sheet thickness is less than the lower limit ofthe above range, the sheets are inferior in portability and cracks aretherefore formed in the sheets. In contrast, when the sheet thickness ismore than the upper limit of the above range, walls of the sheets cannotbe processed by the photolithographic process. Thus, the sheet thicknessoutside the above range is not preferable. The substrate including thestacked sheets preferably has a thickness of 50 to 3000 μm (morepreferably 100 to 2500 μm and further more preferably 400 to 2000 μm).When the substrate thickness is less than the lower limit of the aboverange, unevenness in thickness occurs in the stacking step. In contrast,when the substrate thickness is more than the upper limit of the aboverange, the substrate cannot be uniformly fired because the organiccomponent remains inside the substrate and is gasified in the firingstep; hence, cavities are caused in the substrate by the resultingcomponent. Thus, the substrate thickness outside the above range is notpreferable.

[0114] In the present invention, the step of firing the stacked ceramicgreen sheets includes a sub-step of placing the stacked sheets in afiring furnace such as a muffle furnace to gasify the organic componentremaining in the sheets, the sub-step being usually referred to as adegreasing sub-step. The step further includes a sub-step of allowing atleast one or more inorganic compounds to migrate to partiallycrystallize the compounds, this sub-step being performed after thedegreasing sub-step and usually referred to as a firing or sinteringsub-step.

[0115] In the manufacturing method of the present invention, the sheetsare preferably stacked such that there are substantially no outer facesthat face each other and are arranged substantially in parallel to thenormal line of the principal face of the ceramic multilayer substrate,the outer faces being different from faces between the stacked sheets.In the present invention, the photosensitive green sheets trimmed by thephotolithographic process preferably have an area that is less than orequal to that of outer regions of sheets placed at a lower portion ofthe substrate. This is because deformation hardly occurs in the firingstep and the reproducibility of the shape is high. In the presentinvention, the lower sheets are principally defined as sheets stacked inadvance. In the completed multilayer substrate, the lower sheets areplaced at the side opposite to that of the electronic circuit.

[0116] The term “there are substantially no outer faces” means thatthere are an extremely small number of the outer faces that face eachother and are arranged substantially in parallel. The area of the outerfaces is not particularly limited and is preferably 250000 μm² or less.Alternatively, the outer faces facing each other preferably have a widthof 1000 μm or less when the width is measured in the direction parallelto the normal line perpendicular to a face that is adjacent to andsubstantially perpendicular to the outer faces, wherein the width can beassumed to be the shortest distance between faces that are adjacent toand substantially perpendicular to the outer faces facing each other.Alternatively, a face of which the width is more than 1000 μm preferablyhas a length of 500 μm or less, the width being measured in thedirection perpendicular to the principal face of the substrate.

[0117] In the photosensitive green sheets trimmed by thephotolithographic process and the lower sheets, when patterns of mostouter regions and/or inner end regions are different from each other,the following formula is preferably satisfied:

0.01≦A/B≦0.90

[0118] wherein A represents the area of each photosensitive green sheetand B represents the area of each lower sheet. The value of A/B is morepreferably 0.25 to 0.75.

[0119] In the firing step, the stacked ceramic green sheets arepreferably fired such that the sheets are not shrunk. This is becausethe non-shrinkage firing does not cause distortion and breakage in thecircuit but allows the shape of the sheets, precisely trimmed by thephotolithographic process, to be maintained; hence, a difference in thedesign shape and the shape of the fired sheets can be reduced.

[0120] In the non-shrinkage firing, the fired substrate has a shrinkageof 15% or less in the X-axis direction and also in the Y-axis directionwhen a face of the substrate is defined using the X-Y coordinate plane.In usual isotropic shrinkage, the shrinkage of a side is 10% to 15%.Therefore, if the shrinkage can be controlled within 5% or less, thedistortion and breakage of the circuit can be efficiently prevented.When the green sheets are fired in such a manner that each green sheetis placed between, for example, binding sheets containing asintering-resistant ceramic component, the shrinkage is prevented in thedirection perpendicular to the X-Y plane; however, the shrinkageunavoidably occurs due to the composition of the composite, componentsin the composite, and firing conditions. Thus, if the shrinkage can becontrolled within 1% or less, non-shrinkage can be assumed to beachieved. The shrinkage is more preferably 0.5% or less and further morepreferably 0.1% or less. Such conditions are applicable to coatings,which can be fired in such a manner that such a binder sheet is placedon the upper face of each coating.

[0121] As described above, the multilayer substrate can be preparedaccording to the following procedure: the photosensitive ceramiccomposite is formed into the green sheets, which are trimmed by thephotolithographic process, stacked, and then fired. Known glass ceramicsubstrates cannot be precisely processed, whereas the multilayersubstrate can be done. As described as the object, the multilayersubstrate is fit for a housing of a mobile electronic apparatus and canbe placed in such a housing having a small packaging volume. When themultilayer substrate has a simple rectangular parallelepiped shape, thesubstrate cannot be placed in the housing. However, in the multilayersubstrate, particular portions can be precisely removed freely.Furthermore, electronic circuits can be formed in the perforatedstructures.

EXAMPLES

[0122] The present invention will now be described in detail withreference to examples. The present invention is not limited to theexamples.

[0123] (1) Enhancement of Photolithographic Properties by Use ofLow-refractive Index Material

[0124] The refractive index is a measurement obtained using the sodium Dline unless otherwise specified. Inorganic particles and an organiccomponent used in the examples are described below.

[0125] A. Inorganic Particles

[0126] Inorganic Particles I:

[0127] Ceramic particle mixture consisting of 49.8% of alumina particlesand 50.2% of glass particles

[0128] Characteristics of the alumina particles: an average particlesize of 2 μm and a refractive index of 1.78 (a measurement obtainedusing the sodium D line)

[0129] Composition of the glass particles: 10.8% of Al₂O₃, 51.5% ofSiO₂,15.6% of PbO, 7.1% of CaO, 2.86% of MgO, 3% of Na₂O, 2% of Ka₂O,and, 5.3% of B₂O₃

[0130] Characteristics of the glass particles: a glass transition pointof 565° C., a thermal expansion coefficient of 60.5×10 ⁻⁷/K, adielectric constant of 8.0 (1 MHz), an average particle size of 2 μm,and a refractive index of 1.58 (a measurement obtained using the sodiumD line)

[0131] Inorganic Particles II:

[0132] Al₂O₃—SiO₂—B₂O₃ glass particles

[0133] Composition of the glass particles: 8.7% of Al₂O₃, 67% of SiO₂,2.7% of ZrO₂, 1.6% of Ka₂O, and 12.5% of B₂O₃

[0134] Characteristics of the glass particles: a glass transition pointof 500° C., a thermal expansion coefficient of 42×10⁻⁷/K, a dielectricconstant of 4.7 (1 MHz), an average particle size of 3 μm, and arefractive index of 1.68

[0135] B. Different Surface Material Placed on Inorganic ParticleSurface

[0136] In order to coat inorganic particles with a solution, organosolwas prepared and then used. The average particle size of particles inthe organosol was determined with the LB-500 dynamic light-scatteringparticle size distribution analyzer manufactured by Horiba Ltd. Theorganosol was dried and the refractive index thereof was determined byan immersion method.

[0137] Coating Material I: ZrO₂ sol (an average particle size of 12 nm),a γ-butyrolactone solvent, a concentration of 11%, and a refractiveindex of 2.0, the refractive index being measured in a dry state

[0138] Coating Material II: TiO₂ sol (an average particle size of 7 nm),a propylene glycol solvent, a concentration of 21%, and a refractiveindex of 2.3, the refractive index being measured in a dry state

[0139] Coating Material III: CeO₂ sol (an average particle size of 17nm), a benzyl alcohol solvent, a concentration of 12%, and a refractiveindex of 2.3, the refractive index being measured in a dry state

[0140] Coating Material IV: Ta₂O₅ sol (an average particle size of 14nm), a benzyl alcohol solvent, a concentration of 19%, and a refractiveindex of 2.0, the refractive index being measured in a dry state

[0141] Coating Material V: Y₂O₃ sol (an average particle size of 19 nm),a γ-butyrolactone solvent, a concentration of 25%, and a refractiveindex of 2.0, the refractive index being measured in a dry state

[0142] Coating Material VI: ZnS sol (an average particle size of 13 nm),a γ-butyrolactone solvent, a concentration of 18%, and a refractiveindex of 2.2, the refractive index being measured in a dry state

[0143] Coating Material VII: Al₂O₃ sol (an average particle size of 9nm), a propylene glycol solvent, a concentration of 9%, and a refractiveindex of 1.7, the refractive index being measured in a dry state

[0144] Coating Material VIII: CeF₂ sol (an average particle size of 17μm), a butanol solvent, a concentration of 22%, and a refractive indexof 1.6, the refractive index being measured in a dry state

[0145] Coating Material IX: MgF₂ sol (an average particle size of 19nm), an ethanol solvent, a concentration of 14%, and a refractive indexof 1.4, the refractive index being measured in a dry state

[0146] Coating Material X: SiO₂ sol (an average particle size of 8 μm),a γ-butyrolactone solvent, a concentration of 20%, and a refractiveindex of 1.4, the refractive index being measured in a dry state

[0147] C. Photosensitive Organic Component

[0148] Polymer 1: a polymer, having a weight-average molecular weight of43,000 and an acid value of 95, prepared by allowing 0.4 equivalent ofglycidyl methacrylate to react with one equivalent of a carboxyl groupof a copolymer prepared using 40% of methacrylic acid, 30% of methylmethacrylate, and 30% of styrene on a weight basis

[0149] Photoreactive Compound 1: bis(2-hydroxy-3-methacryloyloxypropyl)isopropylamine (GMPA)

[0150] Photoreactive Compound 2: TN-1 (urethane polymer, manufactured byNegami Chemical Industrial Co., Ltd., having a molecular weight of about12,000)

[0151] Photoreactive Compound 3: bis(4-methacryloylthiophenyl) sulfide(high-refractive index monomer MPSMA, manufactured by Sumitomo SeikaChemicals Co., Ltd.)

[0152] Photopolymerization Initiator: IC-369 (Irgacure-369 manufacturedby Chiba Geigy Co., Ltd)

[0153] Solvent: solvent mixture of 90% methyl ethyl ketone and 10%n-butylalcohol

[0154] D. Preparation of Organic Vehicle

[0155] A solvent and a polymer were mixed and the mixture was heated to60° C. while agitated, whereby the polymer was completely dissolved inthe solvent. The solution was cooled to room temperature, and aphotoreactive compound and a photopolymerization initiator weredissolved in the solution. The resulting solution was degassed undervacuum conditions and then filtrated with a 250-mesh filter, whereby anorganic vehicle was prepared. The solution contained 10 parts of thepolymer, 10 parts of the photoreactive compound (the total compoundcontent is employed when a plurality of photoreactive compounds areused), and 3.5 parts of the photopolymerization initiator on a weightbasis.

[0156] E. Treatment of Inorganic Particles

[0157] Sections containing a different surface material were each formedon the surfaces of inorganic particles using the solution. A preparationprocedure was as follows: the inorganic particles used herein and acoating agent were mixed, the mixture was agitated for one hour at roomtemperature, the resulting mixture was filtrated with a sheet of filterpaper (type GF/B, manufactured by Whatman Inc.) by aspiration, and theobtained cake was heated to 500° C. in a muffle furnace.

[0158] The state of the different surface material on the inorganicparticle surface was observed with a scanning electron microscope, andthe thickness of each section containing the different surface materialwas determined with a transmission electron microscope.

[0159] F. Preparation of Paste

[0160] Inorganic particles were blended with the organic vehicle, theblend being hereinafter referred to as powder blend. The powder blendwas wet-mixed for 20 hours in a ball mill, whereby paste was prepared.The amount of the polymer and photoreactive compound, which arecontained in the organic vehicle, was 20 parts by weight and the amountof the powder blend was 80 parts by weight.

[0161] G. Preparation of Green Sheets

[0162] Green sheets were formed in a chamber, shielded from UV rays, bya doctor blade process in such a manner that the distance between apolyester carrier film and a blade is 0.1 to 0.8 mm and the forming rateis 0.2 m/min. The sheet thickness was 100, 150, or 200 μm.

[0163] H. Determination of Light Transmittance

[0164] In order to prepare samples for determining the lighttransmittance, green sheets were prepared in the same manner as theabove. The green sheets had a thickness of 50 μm. Each green sheet wascut into 40-mm square pieces, and the pieces were heated at 80° C. forone hour, whereby a solvent was evaporated. The light transmittance ofthe obtained samples were measured with a haze computer, model HGM-2DP,manufactured by Suga Test Instruments Co. Measurement items are thetotal beam transmittance and the rectilinear beam transmittance. Thetotal beam transmittance is defined as the percentage of the amount oflight, passing through each sample, in the amount of light applied tothe sample. The rectilinear beam transmittance is defined as thepercentage of the amount of light, rectilinearly traveling through eachsample without changing the path, in the amount of light applied to thesample. When the total beam transmittance is high, the clarity is high;hence, exposure light can arrive at a deep area of a sheet having alarge thickness. When the rectilinear beam transmittance is high, apattern of a photomask can be precisely transferred; hence, via-holesformed by exposure and development have substantially a rectangularshape in cross section. An increase in total beam transmittance allowsperforations to be formed in thick sheets and an increase in rectilinearbeam transmittance allows via-holes having a high aspect ratio in crosssection to be formed.

[0165] I. Formation of Via-holes

[0166] The green sheets were each cut into 100-mm square pieces, and thepieces were heated at 80° C. for one hour, whereby a solvent wasevaporated. In order to form a pattern, each piece was exposed for oneminute using an ultra high-pressure mercury vapor lamp having an outputof 15 to 25 mW/cm² in such a manner that a chromium mask having avia-hole diameter of 30 to 100 μm and a via-hole pitch of 500 μm wasdirectly placed on the upper face of the piece and light was appliedthereto. The resulting piece was developed at 25° C. with an aqueoussolution containing 0.5% by weight of monoethanolamine, and formedvia-holes were cleaned using a spray.

[0167] J. Preparation of Binding Sheets Used for Firing

[0168] Paste was prepared by mixing aluminum particles, zirconiaparticles, or magnesia particles with polyvinyl butyral, dioctylphthalate, an organic solvent, and the like. The paste was formed intosheets by a doctor blade process.

[0169] K. Preparation of Multilayer Substrates

[0170] Five or six green sheets containing the photosensitive ceramiccomposite of the present invention were stacked, and the resulting greensheets were placed between binding sheets for non-shrinkage firing andthen heat-pressed at 80° C. with a pressure of 150 kg/cm². The resultingsheets were fired at 900° C. for 30 minutes in an air atmosphere,whereby multilayer substrates were prepared. The shrinkage caused byfiring was measured for the X-Y plane.

[0171] Measurement of Dielectric Constant

[0172] The dielectric constant was measured with a network analyzer andan impedance analyzer or a cavity resonator.

Example 1

[0173] Sections containing a different surface material were formed onthe surfaces of Inorganic Particles I using Coating Material X to beconverted into the different surface material. The resulting particleswere observed with a scanning electron microscope and the observationshowed that SiO₂ derived from Coating Material X was present on theparticle surfaces. Furthermore, the particles were observed with atransmission electron microscope and the observation showed that SiO₂layers had a thickness of 70 nm. The treated particles were used as aninorganic-particle source material.

[0174] Samples for evaluating the light transmittance and green sheetshaving a thickness of 100 μm were prepared using the following materialsand compounds: the inorganic-particle source material (70%), Polymer 1(15%) functioning as a photosensitive organic component, PhotoreactiveCompound 1 (5%), Photoreactive Compound 2 (5%), Photoreactive Compound 3(5%), and a photopolymerization initiator. The measurement of the lighttransmittance showed that each sample had a total beam transmittance of60% and a rectilinear beam transmittance of 6.5%.

[0175] The formation of via-holes was attempted, whereby 30-μm via-holeswere formed in the green sheets. After the resulting sheets were cured,the resulting sheets were placed between alumina binding sheets and thenfired at 900° C. for 30 minutes, whereby a white multilayer substratewas obtained. The substrate had no cracks but had a bending strength of270 MPa. The dielectric constant was 7.8 (1 MHz).

[0176] Furthermore, 200-μm green sheets were prepared. The formation ofvia-holes was attempted, whereby 50-μvia-holes were formed in the greensheets.

Examples 2a to 2h

[0177] The content of the γ-butyrolactone solvent in Coating Material Xused in Example 1 was varied as shown in Table 1. Samples for evaluatingthe light transmittance and green sheets having a thickness of 100 μmwere prepared using resulting Coating Material X. Results shown in Table1 were obtained. TABLE 1 Example Example Example Example Example ExampleExample Example 2a 2b 2c 2d 2e 2f 2g 2h Concentration 3 7 12 20 27 32 3848 (%) Layer Thickness 2 7 50 70 120 190 220 270 (nm) Total Beam 26 3458 60 62 43 28 25 Transmittance (%) Rectilinear Beam 1.5 3.6 7.2 6.5 8.63.8 2.6 1.5 Transmittance (%) Via-hole 100 85 50 30 30 75 100 100Diameter (μm)

[0178] Table 1 shows that light transmission characteristics and avia-hole forming characteristic are varied depending on the change inthe thickness of each section containing the different surface material.

Examples 3a to 3j

[0179] Only the aluminum particles for Inorganic Particles I weretreated with each of Coating Materials I to X and the resulting aluminumparticles were mixed with the glass particles for Inorganic Particles I,whereby a inorganic-particle source material was prepared. In commonwith Example 1, an organic vehicle was prepared and green sheets havinga thickness of 100 μm and samples for evaluating light transmissioncharacteristics were prepared. The evaluation of the light transmissioncharacteristics and the evaluation of a via-hole forming characteristicprovided the results shown in Table 2. TABLE 2 Example Example ExampleExample Example Example Example Example Example Example 3a 3b 3c 3d 3e3f 3g 3h 3i 3j Coating I II III IV V VI VII VIII IX X Material Layer 4090 50 60 100 60 80 110 90 70 Thickness (nm) Total Beam 36 32 35 37 39 3441 55 50 60 Transmittance (%) Rectilinear 4.1 3.2 3.5 4.0 4.2 3.9 5.06.3 6.2 6.5 Beam Transmittance (%) Via-hole 70 80 75 70 70 50 45 30 3030 Diameter (μm)

[0180] Table 2 shows that the light transmission characteristics arehigh and via-holes have a small diameter when a coating materialcontains a different surface material having a refractive index lessthan or equal to the refractive index (1.7 to 1.8) of the aluminumparticles.

Examples 4a to 4g

[0181] In common with Example 1, an inorganic-particle source materialwas prepared by forming sections, containing a different surfacematerial, on the surfaces of inorganic particles except that InorganicParticles II are prepared and then crashed into small particles havingdifferent average particle sizes, and the small particles are treatedwith Coating Material VIII. Samples for evaluating light transmissioncharacteristics and green sheets having a thickness of 100 μm wereprepared and they were subjected to evaluation in the same manner asthat of Example 1. Obtained results are shown in Table 3. TABLE 3Example Example Example Example Example Example Example 4a 4b 4c 4d 4e4f 4g Average 0.11 0.32 0.6 3.4 4.8 8.5 12 Particle Size (μm) Total Beam32 36 42 55 51 40 29 Transmittance (%) Rectilinear 2.9 3.0 4.1 5.2 4.62.8 2.2 Beam Transmittance (%) Via-hole 100 70 50 50 75 90 100 Diameter(μm)

[0182] Table 3 shows that the light transmission characteristics and thediameter of formed via-holes vary depending on the average particlesize. When the average particle size was small, a mixture of aninorganic-particle source material and an organic component hadextremely high viscosity and particles remained on the surfaces of theprepared green sheets. In contrast, when the average particle size waslarge, the green sheets had large irregularities and there were largenumber of openings, formed by the removal of the particles, on walls ofthe via-holes formed by exposure and development.

[0183] (2) Enhancement of Flexibility, Compatibility, and Developability

[0184] A. Photosensitive Organic Component (Sub-component A1)

[0185] Monomer I: para-cumylphenol acrylate modified with ethylene oxide(manufactured by TOAGOSEI Co., Ltd.)

[0186] Monomer II: bisphenol-A diacrylate modified with ethylene oxide(manufactured by TOAGOSEI Co., Ltd.)

[0187] Photopolymerization Initiator:

[0188] 2-benzyl-dimethylamino-1-(4-morpholinophenyl)-butanone-1

[0189] (Sub-component A2)

[0190] Urethane Compound I: a compound, having a molecular weight of19000 and containing 30% of an ethylene oxide unit, represented by thefollowing formula (1′):

CH₂═CR¹COO—R²—(R³—R⁴)_(n)—R³—R²—OCOCR¹═CH₂   (1′)

[0191] wherein R¹ represents hydrogen, R² represents an ethylene oxidegroup, R³ represents an isophorone diisocyanate residue, and R⁴represents an ethylene oxide-propylene oxide cooligomer

[0192] Urethane Compound II: a compound, having a molecular weight of42000, represented by the above formula (1′), wherein R¹ representshydrogen, R² represents a propylene oxide group, R³ represents anisophorone diisocyanate residue, and R⁴ represents a propylene oxideoligomer

[0193] Urethane Compound III: urethane acrylate, UV6100B (manufacturedby Nippon Synthetic Chemical Industry Co., Ltd.)

[0194] (Sub-component A3)

[0195] Polymer I: a copolymer, prepared using 30% of styrene, 30% methylmethacrylate, and 40% of methacrylic acid and modified by allowing oneequivalent of a carboxyl group thereof to react with 0.4 equivalent ofglycidyl methacrylate, having a weight-average molecular weight of 43000and an acid value of 95

[0196] Polymer II: a polymer, Cyclomer P (ACA) 250, manufactured byDaicel Chemical Industries Ltd., having a weight-average molecularweight of 10000 and an acid value of 75, the polymer being prepared byallowing 3,4-epoxycyclohexyl methacrylate to react with a copolymerobtained from methacrylic acid and methyl methacrylate

[0197] B. Inorganic Particles

[0198] Inorganic Particles I:

[0199] Composite ceramic consisting of 49.8% of alumina particles and50.2% of glass particles

[0200] Characteristics of the alumina particles: an average particlesize of 2 μm

[0201] Composition of the glass particles: 10.8% of Al₂O₃, 51.5% ofSiO₂, 15.6% of PbO, 7.1% of CaO, 2.86% of MgO, 3% of Na₂O, 2% of K₂O,and 5.3% of B₂O₃

[0202] Characteristics of the glass particles: a glass transition pointof 565° C., a thermal expansion coefficient of 60.5×10⁻⁷/K, a dielectricconstant of 8.0 (1 MHz), and an average particle size of 2 μm

[0203] Inorganic Particles II:

[0204] Al₂O₃—SiO₂—B₂O₃ glass particles

[0205] Composition of the glass particles: 8.7% of Al₂O₃, 67% of SiO₂,2.7% of ZrO₂, 1.6% of K₂O, and 12.5% of B₂O₃

[0206] Characteristics of the glass particles: a glass transition pointof 500° C., a thermal expansion coefficient of 42×10⁻⁷/K, a dielectricconstant of 4.7 (1 MHz), and an average particle size of 3 μm

[0207] Inorganic Particles III:

[0208] Composite ceramic consisting of 85% of Al₂O₃—SiO₂—B₂O₃ glassparticles and 15% of quartz particles

[0209] Composition of the glass particles: 1.87% of Al₂O₃, 67.3% ofSiO₂, 1.22% of K₂O, and 11.8% of B₂O₃

[0210] Characteristics of the glass particles: a glass transition pointof 507° C., a thermal expansion coefficient of 46×10⁻⁷/K, a dielectricconstant of 4.6 (1 MHz), and an average particle size of 2.2 μm

[0211] Inorganic Particles IV:

[0212] Al₂O₃—SiO₂—B₂O₃ composite ceramic

[0213] Composition of the ceramic: 0.34% of Al₂O₃, 84.3% of SiO₂, 1.29%of K₂O, and 11.7% of B₂O₃

[0214] Characteristics of the ceramic: a glass transition point of 509°C., a thermal expansion coefficient of 22×10⁻⁷/K, a dielectric constantof 4.5 (1 MHz), and an average particle size of 2.5 μm

[0215] Inorganic Particles V:

[0216] Composite ceramic (NKX-592J, manufactured by Nippon Ferro Co.,Ltd.) consisting of 50% of alumina particles and 50% of glass particles

[0217] Characteristic of the alumina particles: an average particle sizeof 2 μm

[0218] Composition of the glass particles: Al₂O₃—B₂O₃—SiO₂—CaO glass

[0219] Characteristic of the glass particles: an average particle sizeof 4.8 μm

[0220] Inorganic Particles VI:

[0221] Alumina-crystalline glass composite ceramic (FJ352J, manufacturedby Nippon Ferro Co., Ltd.)

[0222] Composition of the glass particles: Al₂O₃—B₂O₃—SiO₂—CaO—ZnO glass

[0223] Characteristic of the glass particles: a glass transition pointof 683° C., a thermal expansion coefficient of 52×10⁻⁷/K, and an averageparticle size of 5 μm

[0224] Inorganic Particles VII:

[0225] Crystalline glass (FJ351J, manufactured by Nippon Ferro Co.,Ltd.)

[0226] Composition of the glass particles: Al₂O₃—B₂O₃—SiO₂—MgO glass

[0227] Characteristic of the glass particles: a glass transition pointof 681° C., a thermal expansion coefficient of 90×10⁻⁷/K, and an averageparticle size of 5 μm

[0228] Inorganic Particles VIII:

[0229] Non-crystalline glass (K805, manufactured by Asahi Techno GlassCorporation)

[0230] Composition of the glass particles: Al₂O₃—B₂O₃—SiO₂ glass

[0231] Inorganic Particles IX:

[0232] Mixture consisting of 80% of glass particles and 20% of SiO₂particles

[0233] Composition of the glass particles: Al₂O₃—B₂O₃—SiO₂ glass

[0234] C. Developing Solution

[0235] Developing Solution I: a 1.5% solution of sodium carbonate inwater

[0236] Developing Solution II: a 0.5% solution of n-propylamine in water

[0237] Developing Solution III: a 0.5% solution of 2-aminoethanol inwater

[0238] D. Preparation of Organic Vehicle

[0239] A polymer was mixed with a solvent and the mixture was heated to60° C. while agitated, whereby the polymer was completely dissolved inthe solvent. The solution was cooled to room temperature, and a urethanecompound, a monomer, and a photopolymerization initiator were dissolvedin the resulting solution. The resulting solution was degassed undervacuum conditions and then filtrated with a 250-mesh filter, whereby anorganic vehicle was prepared.

[0240] E. Preparation of Paste

[0241] Inorganic particles were mixed with the organic vehicle, themixture was wet-mixed for 20 hours in a ball mill, whereby slurry orpaste was prepared. The slurry or paste contained 30 parts of theorganic vehicle containing a photosensitive organic component and 70parts of an inorganic component on a weight basis.

[0242] F. Preparation of Green Sheets

[0243] Green sheets were formed in a chamber, shielded from UV rays, bya doctor blade process in such a manner that the distance between apolyester carrier film and a blade is 0.1 to 0.8 mm and the forming rateis 0.2 m/min. The sheet thickness was 150 μm.

[0244] G. Formation of Via-holes

[0245] Each green sheet was cut into 100-mm square pieces, and thepieces were heated at 80° C. for one hour, whereby a solvent wasevaporated. In order to form a pattern, each piece was exposed for oneminute using an ultra high-pressure mercury vapor lamp having an outputof 15 to 25 mW/cm² in such a manner that a chromium mask having avia-hole diameter of 30 to 100 μm and a via-hole pitch of 500 μm wasdirectly placed on the upper face of the piece and light was appliedthereto. The resulting piece was developed with a developing solutionmaintained at 25° C., and formed via-holes were cleaned using a spray.

[0246] H. Determination of Variation

[0247] A pattern having a line width of 75 μm and a line pitch of 150 μmwas formed on each green sheet having a thickness of 150 μm. An upperportion of a cross section of the resulting sheet was observed with ascanning electron microscope, the variation was measured along a linehaving a length of about 1 mm, and values of three samples wereaveraged.

[0248] I. Preparation of Binding Sheets Used for Firing

[0249] Paste was prepared by mixing aluminum particles, zirconiaparticles, or magnesia particles with polyvinyl butyral, dioctylphthalate, an organic solvent, and the like. The paste was formed intosheets by a doctor blade process.

[0250] J. Preparation of Multilayer Substrates

[0251] Five or six green sheets containing the photosensitive ceramiccomposite of the present invention were stacked, and the resulting greensheets were placed between binding sheets for non-shrinkage firing andthen heat-pressed at 80° C. with a pressure of 150 kg/cm². The resultingsheets were fired at 900° C. for 30 minutes in an air atmosphere,whereby multilayer substrates were prepared. The shrinkage caused byfiring was measured for the X-Y plane.

[0252] K. Determination of Tensile Strength and Elongation of GreenSheets

[0253] Each green sheet was irradiated with activation rays with anoptimum exposure value, whereby the sheet was cured. The resulting sheetwas dried at 80° C. for 15 minutes. The following median was used forthe optimum exposure value: the median of exposure values fit to formvia-holes in sheets containing a photosensitive ceramic compositeprepared by mixing inorganic particles and a photosensitive organiccomponent. Obtained test pieces were dumbbell-shaped and had a width of10 to 25 mm, a length of 40 to 100 mm, and a thickness of 0.1 to 0.2 mm.The test pieces were measured for tensile strength and elongationaccording to JIS K6301 using a tensile strength tester under thefollowing conditions: a stretching rate of 50 mm/min, a temperature of23° C., and a relative humidity of 50%. An average of measurements often test pieces was employed.

[0254] L. Determination of Dielectric Constant

[0255] The dielectric constant was measured with a network analyzer andan impedance analyzer or a cavity resonator.

[0256] M. Determination of Bending Strength and Cracks

[0257] The flexural strength was measured by a bending strength testmethod (JIS R1601). Surfaces of the test pieces were visually observedand the number of cracks were counted.

Example 5

[0258] Green sheets having a thickness of 150 μm were prepared usingpaste containing 70% of Inorganic Particles I, 15% of Polymer Ifunctioning as a photosensitive organic component, 2% of UrethaneCompound I, 5% of Monomer I, and a photopolymerization initiator. Theformation of via-holes was attempted, whereby 75-μm via-holes wereformed. Developing Solution I was used for the development. The haze ofthe photosensitive organic component was 0.1. The variation in line sizewas 1.2. The sheets were cured and then fired at 900° C. for 30 minutesusing the alumina binding sheets, whereby a white multilayer substratewas obtained. The substrate had no cracks but had a bending strength of270 MPa and a dielectric constant of 7.8 (1 MHz). The cured sheets had atensile strength of 0.6 N/mm² and an elongation of 20%.

Examples 6 to 17

[0259] The procedure described in Example 5 was repeated using thecomponents shown in Table 4. Test results are shown in Table 4. Sampleshave a small change in size and high strength.

Comparative Example 1

[0260] The procedure shown in Example 1 was repeated using pastecontaining 70% of Inorganic Particles I, 15% of Polymer I functioning asa photosensitive organic component, 2% of Urethane Compound I, 5% ofMonomer I, and a photopolymerization initiator. Obtained sheets had athickness of 150 μm, and Developing Solution III was used. The sheetshad a change in size of 2.0, that is, the sheets were seriously swollen.The sheets were fired using the alumina binder sheets, whereby a whitemultilayer substrate was prepared. The substrate had cracks therein andhad a bending strength of 150 MPa and a dielectric constant of 7.0 (1MHz). The sheets cured or non-cured had a tensile elasticity modulus of0.2 N/mm² and an elongation of 5%. The sheets and the substrate hadinsufficient strength.

Comparative Example 2

[0261] The procedure shown in Example 1 was repeated using pastecontaining 70% of Inorganic Particles I, 15% of polymer I functioning asa photosensitive organic component, 2% of Urethane Compound II, 5% ofMonomer I, and a photopolymerization initiator. Obtained sheets had achange in size of 1.8, that is, the sheets were seriously swollen. Thesheets were fired using the alumina binder sheets, whereby a whitemultilayer substrate was prepared. The substrate had cracks therein andhad a bending strength of 100 MPa and a dielectric constant of 6.5 (1MHz). The sheets cured or non-cured had a tensile elasticity modulus of0.1 N/mm² and an elongation of 3%. The sheets and the substrate hadinsufficient strength. TABLE 4 Example 5 Example 6 Example 7 Example 8Example 9 Polymer Type I I I I I Pats by 15 15 15 15 15 Weight UrethaneType I I I I I Compound Pats by 2 2 2 2 2 Weight Monomer Type I I I I IPats by 5 5 5 5 5 Weight Inorganic Type I II III IV V particles Pats by70 70 70 70 70 Weight Developing Type I I I I I Solution Dimensional 1.21.1 1 1.2 1.1 Change Haze 0.2 0.2 0.2 0.2 0.2 Photocured Tensile 0.580.61 0.6 0.62 0.64 Sheet Strength (N/mm²) Elongation 18 20 19 19 20 (%)Fired Dielectric 7.8 4.6 4.5 4.8 6.5 Sheet Constant (1 MHz) Bending 270150 150 155 200 Strength of White Substrate (MPa) Cracks 0 0 0 0 0(Number) Example Example Example Example Example 10 11 12 13 14 PolymerType I I I I I Pats by 15 15 15 15 15 Weight Urethane Type I I I I ICompound Pats by 2 2 2 2 2 Weight Monomer Type I I I I I Pats by WeightInorganic Type VI VII VII IX I particles Pats by 70 70 70 70 70 WeightDeveloping Type I I I I I Solution Dimensional 1.3 1.3 1.1 1.2 1.2Change Haze 0.2 0.2 0.2 0.2 0.2 Photocured Tensile 0.64 0.64 0.6 0.640.59 Sheet Strength (N/mm²) Elongation 20 20 21 19 20 (%) FiredDielectric 7.4 6.5 5 4.5 7.8 Sheet Constant (1 MHz) Bending 250 200 150130 270 Strength of White Substrate (MPa) Cracks 0 0 0 0 0 (Number)Example Example Example Comparative Comparative 15 16 17 Example 1Example 2 Polymer Type II I I I I Pats by 15 15 15 15 15 Weight UrethaneType I III III I II Compound Pats by 2 2 2 2 2 Weight Monomer Type I IIII I I Pats by 5 5 5 5 5 Weight Inorganic Type I I I I I particles Patsby 70 70 70 70 70 Weight Developing Type I I II III III SolutionDimensional 1.2 1.2 1.1 2 1.8 Change Haze 0.1 0.1 0.1 0.1 10 PhotocuredTensile 0.62 0.64 0.64 0.2 0.1 Sheet Strength (N/mm²) Elongation 21 2222 5 3 (%) Fired Dielectric 7.8 7.8 7.8 7.0 6.5 Sheet Constant (1 MHz)Bending 270 270 270 150 100 Strength of White Substrate (MPa) Cracks 0 00 10 20 (Number)

[0262] (3) Processing Method, Manufacturing Method, and Performance ofMultilayer Substrate Obtained by the Methods

[0263] Components of a photosensitive ceramic composite will now bedescribed.

[0264] A. Inorganic Powdery Component

[0265] An inorganic powdery component was prepared using a combinationof inorganic particles having an average particle size of about 2 μm andfine particles having an average particle size of about 10 nm.

[0266] (Inorganic Particles)

[0267] The inorganic sub-components described below were used. Theaverage particle size thereof was measured by a laser diffractionscattering method using an analyzer, Microtrac 9320 HRA (X-100),manufactured by Nikkiso Co., Ltd.

[0268] Inorganic Sub-component 1: BaO—SiO₂—Al₂O₃—CaO—B₂O₃ crystallizedglass particles having an average particle size of 2.3 μm

[0269] Inorganic Sub-component 2: a mixture consisting of 30% of silicaparticles and 70% of borosilicate glass particles containing 44% ofSiO₂, 29% of Al₂O₃, 11% of MgO, 7% of ZnO, and 9% of B₂O₃ on a weightbasis, the average particle size of the mixture being 2.0 μm

[0270] Inorganic Sub-component 3: a mixture consisting of 50% by weightof borosilicate glass particles having the same composition as that ofInorganic Sub-component 2 and 50% by weight of spherical amorphoussilica particles having an average particle size of 2 μm, the averageparticle size of the mixture being 1.9 μm

[0271] Inorganic Sub-component 4: a mixture consisting of 45% of quartzparticles, 20% of cordierite particles, and 35% of borosilicate glassparticles having the same composition as that of Inorganic Sub-component2 on a weight basis

[0272] Inorganic Sub-component 5: a mixture consisting of 32% ofamorphous silica particles, 23% of alumina-magnesia spinel particles,and 45% of borosilicate glass particles on a weight basis

[0273] Inorganic Sub-component 6: a mixture consisting of 48% by weightof glass particles and 52% by weight of alumina particles, wherein theglass particles contain 34.5% of Al₂O₃, 38.2% of SiO₂, 9.2% of B₂O₃,5.1% of BaO, 4.8% of MgO, 4.4% of CaO, and 2.1% of TiO₂ on a weightbasis; the mixture has an average particle size of 2.2 μm; the aluminaparticles have an average particle size of 2.1 μm; the glass particleshave a refractive index of 1.584, a sphericity of 80%, an averageparticle size of 2.5 μm, a maximum particle size of 13.1 μm, a specificsurface area of 2.41 m²/g, a glass transition point of 652° C., and asoftening point of 746° C.

[0274] (Inorganic Fine Particles)

[0275] The inorganic fine particles described below were used.

[0276] Fine Particles 1: silica fine particles having an averageparticle size of 0.005 μm

[0277] Fine Particles 2: silica fine particles having an averageparticle size of 0.011 μm

[0278] Fine Particles 3: silica fine particles having an averageparticle size of 0.025 μm

[0279] Fine Particles 4: silica fine particles having an averageparticle size of 0.045 μm

[0280] Fine Particles 5: silica fine particles having an averageparticle size of 0.065 μm

[0281] Fine Particles 6: silica fine particles having an averageparticle size of 0.095 μm

[0282] Fine Particles 7: alumina fine particles having an averageparticle size of 0.010 μm

[0283] Fine Particles 8: alumina fine particles having an averageparticle size of 0.035 μm

[0284] Fine Particles 9: alumina fine particles having an averageparticle size of 0.043 μm

[0285] Fine Particles 10: alumina fine particles having an averageparticle size of 0.070 μm

[0286] Fine Particles 11: alumina fine particles having an averageparticle size of 0.094 μm

[0287] Fine Particles 12: zirconia fine particles having an averageparticle size of 0.024 μm

[0288] Fine Particles 13: titania fine particles having an averageparticle size of 0.014 μm

[0289] Fine Particles 14: yttria fine particles having an averageparticle size of 0.008 μm

[0290] Fine Particles 15: ceria fine particles having an averageparticle size of 0.029 μm

[0291] Fine Particles 16: magnesia fine particles having an averageparticle size of 0.037 μm

[0292] B. Photosensitive Organic Component

[0293] (Sub-component 1)

[0294] Monomer I: para-cumylphenol acrylate modified with ethylene oxide(manufactured by TOAGOSEI Co., Ltd.)

[0295] Monomer II: bisphenol-A diacrylate modified with ethylene oxide(manufactured by TOAGOSEI Co., Ltd.)

[0296] Photopolymerization Initiator:

[0297] 2-benzyl-dimethylamino-1-(4-morpholinophenyl)-butanone-1

[0298] (Sub-component 2)

[0299] Urethane Compound I: a compound, having a molecular weight of19000 and containing 30% of an ethylene oxide unit, represented by thefollowing formula (1′):

CH₂═CR¹COO—R²—(R³—R⁴ )_(n)—R³—R²—OCOCR¹═CH₂   (1′)

[0300] wherein R¹ represents hydrogen, R² represents an ethylene oxidegroup, R³ represents an isophorone diisocyanate residue, and R⁴represents an ethylene oxide-propylene oxide cooligomer

[0301] Urethane Compound II: a compound, having a molecular weight of42000, represented by the above formula (1′), wherein R¹ representshydrogen, R² represents a propylene oxide group, R³ represents anisophorone diisocyanate residue, and R⁴ represents a propylene oxideoligomer

[0302] Urethane Compound III: urethane acrylate, UV6100B, manufacturedby Nippon Synthetic Chemical Industry Co., Ltd.

[0303] (Sub-component 3)

[0304] Polymer I: a copolymer, prepared using 30% of styrene, 30% methylmethacrylate, and 40% of methacrylic acid and modified by allowing oneequivalent of a carboxyl group thereof to react with 0.4 equivalent ofglycidyl methacrylate, having a weight-average molecular weight of 43000and an acid value of 95

[0305] Polymer II: a polymer, Cyclomer P (ACA) 250, manufactured byDaicel Chemical Industries Ltd., having a weight-average molecularweight of 10000 and an acid value of 75, the polymer being prepared byallowing 3,4-epoxycyclohexyl methacrylate to react with a copolymerobtained from methacrylic acid and methyl methacrylate

[0306] C. Preparation of Organic Vehicle

[0307] A solvent and a polymer were mixed and the mixture was heated to60° C. while agitated, whereby the polymer was completely dissolved inthe solvent. The solution was cooled to room temperature, and an urethancompound, a monomer, and a photopolymerization initiator were dissolvedin the solution. The resulting solution was degassed under vacuumconditions and then filtrated with a 250-mesh filter, whereby an organicvehicle was prepared.

[0308] D. Preparation of Slurry or Paste

[0309] An inorganic component was added to the above organic vehicle,and the they were wet-mixed in a ball mill for 20 hours, whereby slurryor paste was prepared. The prepared slurry or paste had a viscosity ofabout 25 Pa·s unless otherwise specified.

[0310] E. Preparation of Green Sheets

[0311] Green sheets were formed in a chamber, shielded from UV rays, bya doctor blade process in such a manner that the distance between apolyester carrier film and a blade is 0.1 to 0.8 mm and the forming rateis 0.2 m/min. The sheet thickness was 100 or 150 μm.

[0312] F. Formation of Outer Shape Pattern

[0313] Outer Shape

[0314] Test Pattern 1

[0315] Test Pattern 1 was formed on 100-mm square sheets in such amanner that 5-mm square sections each having seven square openings withthe following size were arranged on each sheet at a pitch of 10 mm: asize of 50-μm, 100-μm, 150-μm, 200-μm, 300-μm, 500-μm, or 1-mm square.The openings were present at the center area of each section.

[0316] Test Pattern 2

[0317] Test Pattern 2 was formed on 100-mm square sheets in such amanner that 5-mm square sections each having seven independent squareportions with the following size were arranged on each sheet at a pitchof 10 mm: a size of 50-μm, 100-μm, 150-μm, 200-μm, 300-μm, 500-μm, or1-mm square.

[0318] G. Trimming

[0319] (Photolithographic Process)

[0320] The green sheets were each cut into 100-mm square pieces, and thepieces were heated at 80° C. for one hour, whereby a solvent wasevaporated. In order to form a pattern, each piece was exposed using anultra high-pressure mercury vapor lamp having an output of 15 to 25mW/cm² in such a manner that a chromium mask having one of the testpatterns described above was directly placed on the upper face of thepiece and light was applied thereto. The resulting piece was developedat 25° C. with an aqueous solution containing 0.5% by weight ofmonoethanolamine, and formed via-holes were cleaned using a spray.

[0321] (Punching Process)

[0322] Punching dies were prepared based on the above test patterns. The100-mm square pieces obtained from the green sheets were each punchedwith the corresponding punching dies.

[0323] H. Preparation of Binding Sheets Used for Firing

[0324] Paste was prepared by mixing aluminum particles, zirconiaparticles, or magnesia particles with polyvinyl butyral, dioctylphthalate, an organic solvent, and the like. The paste was formed intosheets by a doctor blade process.

[0325] I. Preparation of Multilayer Substrate

[0326] Among the green sheets containing the photosensitive ceramiccomposite of the present invention, three non-trimmed sheets werestacked and two trimmed sheets were stacked thereon. The resultingsheets were placed between binding sheets for non-shrinkage firingunless otherwise specified. The stacked sheets were heat-pressed at 80°C. with a pressure of 150 kg/cm². The resulting sheets were fired at900° C. for 30 minutes in an air atmosphere, whereby multilayersubstrates were prepared. The shrinkage caused by firing was measuredfor the X-Y plane.

[0327] In tables below, each sheet having a thickness (thicknesspattern) of 100 or 150 μm is represented by symbol A or B, respectively,and the sheets are described from the top. When, for example, the sheetshaving a thickness of 100, 100, 150, 150, or 150 μm are arranged fromthe top in that order, the arrangement is described as “AABBB”.

[0328] J. Evaluation of Prepared Substrate

[0329] The sintered substrates were visually evaluated for distortionand warpage. In order to evaluate the reproducibility of an outer shapepattern, the processed substrates were observed with a metallurgicalmicroscope and a scanning electron microscope. Furthermore, in order toevaluate the cross-sectional shape, the substrates were observed with ascanning electron microscope. In order to evaluate the difference inpitch between patterns, a pattern on each substrate was observed with alaser microscope.

Examples 18a to 18d and Comparative Example 3

[0330] In order to compare the outer shape formed by thephotolithographic process with the outer shape formed by the punchingprocess, samples were tested. Test results are shown in Table 5. Whenthe photolithographic process was used, patterns having a side with alength of at least 100 μm can be precisely formed and substrates havingno warpage can be obtained. In contrast, when the punching process wasused, patterns, similar to Pattern 1, having portions with a length ofless than 250 μm cannot be formed and patterns, similar to Pattern 2,having portions with a length of less than 500 μm cannot be also formed.Thus, fine patterns can be formed on the substrates when thephotosensitive ceramic composite and the photolithographic process areused.

[0331] When patterns similar to Pattern 2 are formed by thephotolithographic process, the carrier film can be used as atransferring sheet; hence, misalignment can be prevented in the stackingstep. In contrast, when such patterns are formed by the punchingprocess, the following problems arise: a punching head is shaken and alarge amount of manpower is needed to align the independent portions ofthe sheets in the stacking step and accuracy in alignment is one orderof magnitude lager than that of patterns formed by the photolithographicprocess, as shown in Table 5. TABLE 5 Manufacturing ConditionsComposition of Inorganic Components Inorganic Composition of InorganicFine Organic Components Particles Particles Component ComponentComponent and and 1 and 2 and 3 and Content Content Content ContentContent Sheet (wt %) (wt %) (wt %) (wt %) (wt %) Arrangement TrimmingExample 18a IS*¹ 1 Fine Monomer I Urethane Polymer I BBBBBPhotolithographic (70) Particles (15) and Compound (5) Process 3 (5)PI*² (3) I (2) Example IS*¹ 2 Fine Monomer I Urethane Polymer I BBBBBPhotolithographic 18b (70) Particles (15) and Compound (5) Process 7 (5)PI*² (3) I (2) Example 18c IS*¹ 4 Fine Monomer I Urethane Polymer IBBBBB Photolithographic (70) Particles (15) and Compound (5) Process 12(5) PI*² (3) I (2) Example IS*¹ 6 Fine Monomer I Urethane Polymer IBBBBB Photolithographic 18d (70) Particles (15) and Compound (5) Process8 (5) PI*² (3) I (2) Comparative IS*¹ 6 Fine Monomer I Urethane PolymerI BBBBB Punching Process Example 3 (70) Particles (15) and Compound (5)8 (5) PI*² (3) I (2) Inspection Results Warpage and ShrinkageReproducible Pattern Misalignment Distortion (%) Pattern 1 Pattern 2(μm) Example 18a Not Observed 0.4 100 μm or more 100 μm or more 2.1Example 18b Not Observed 0.7 100 μm or more  50 μm or more 1.9 Example18c Not Observed 0.1  50 μm or more 100 μm or more 0.9 Example 18d NotObserved 0.07  50 μm or more  50 μm or more 2.2 Comparative Not Observed0.07 250 μm or more 500 μm or more 23 Example 3

Examples 19a to 19d

[0332] Non-trimmed sheets used in the stacking step were investigatedfor difference due to the photosensitivity. The same inorganic componentas that contained in trimmed sheets was mixed with polyvinyl butyral anddioctyl phthalate, whereby paste was prepared. The paste was formed intosheets having a thickness of 200 μm by a doctor blade process. Thosesheets are referred to as non-photosensitive sheets. Test results areshown in Table 6. As shown in Table 6, the non-photosensitive sheets aswell as photosensitive sheets can be stacked and also fired. TABLE 6Manufacturing Conditions Composition of Inorganic Components InorganicComposition of Inorganic Fine Organic Components Particles ParticlesComponent Component Component and and 1 and 2 and 3 and Content ContentContent Content Content Sheet (wt %) (wt %) (wt %) (wt %) (wt %) StackedSheets Arrangement Example 19a IS*¹ 1 Fine Monomer I Urethane Polymer IPhotosensitive AABBB (70) Particles (15) and Compound (5) Sheets 3 (5)PI*² (3) I (2) Example 19b IS*¹ 1 Fine Monomer I Urethane Polymer I Non-AABBB (70) Particles (15) and Compound (5) photosensitive 3 (5) P*² (3)I (2) Sheets Example IS*¹ 4 Fine Monomer I Urethane Polymer IPhotosensitive ABBBB 19c (70) Particles (15) and Compound (5) Sheets 12(5) PI*² (3) I (2) Example IS*¹ 4 Fine Monomer I Urethane Polymer I Non-AABBB 19d (70) Particles (15) and Compound (5) photosensitive 12 (5)PI*² (3) I (2) Sheets Inspection Results Warpage and ShrinkageReproducible Pattern Misalignment Distortion (%) Pattern 1 Pattern 2(μm) Example 19a Not Observed 0.4 100 μm or more 100 μm or more 2.1Example 19b Not Observed 0.4 100 μm or more 100 μm or more 2.2 Example19c Not Observed 0.1  50 μm or more 100 μm or more 0.9 Example 19d NotObserved 0.1  50 μm or more 100 μm or more 1.2

Examples 20a and 20b

[0333] The sheets, prepared in Example 18d and trimmed, having the500-μm square portions or 1-mm square portions of Pattern 2 were stackedand then fired. Test results are shown in Table 7. When each sheethaving the 1-mm square portion is placed on each sheet having the 500-μmsquare portion, distortion occurs in the boundary between the 1-mmsquare portion and the 500-μm square portion as shown in Table 7. Thisis because distortion is prevented from occurring in the sheet havingthe 1-mm square portion by a binding sheet. Thus, a substrate havingsatisfactory properties can be prepared by stacking the sheets with thesquare portion having a size less than or equal to that of the squareportion of the sheets placed at a lower position. TABLE 7 ManufacturingConditions Composition of Inorganic Components Inorganic Composition ofInorganic Fine Organic Components Particles Particles ComponentComponent Component and and 1 and 2 and 3 and Content Content ContentContent Content Sheet (wt %) (wt %) (wt %) (wt %) (wt %) ArrangementExample 20a IS*¹ 6 Fine Monomer I Urethane Polymer I AAAAA (70)Particles (15) and Compound (5) 8 (5) PI*² (3) I (2) Example 20b IS*¹ 6Fine Monomer I Urethane Polymer I AAAAA (70) Particles (15) and Compound(5) 8 (5) PI*² (3) I (2) Manufacturing Conditions Inspection ResultsStacking Order Warpage and Distortion Example 20a Binding Sheet/SheetHaving 500-μm Square Not Observed Portion/Sheet Having 1-mm SquarePortion/ Non-trimmed Sheet/Binding Sheet Example 20b Binding Sheet/SheetHaving 1-mm Square Distortion and cracks were Portion/Sheet Having500-μm Square observed at the boundary Portion/Non-trimmed Sheet/Bindingbetween the 1-mm square Sheet portion and the 500-μm square portion.

Examples 21a to 21l

[0334] In order to evaluate the effect of the binding sheets, a changein the shape of trimmed ceramic substrates was investigated. Test itemsand results are shown in Table 8, which shows that distortion andwarpage can be prevented from occurring, the preciseness of the outerpattern can be enhanced, and misalignment can be prevented fromoccurring by performing non-shrinkage firing using the binding sheets.TABLE 8 Manufacturing Conditions Composition of Inorganic ComponentsInorganic Composition of Inorganic Fine Organic Components ParticlesParticles Component Component Component and and 1 and 2 and 3 andContent Content Content Content Content Sheet (wt %) (wt %) (wt %) (wt%) (wt %) Arrangement Binding Sheet Example 21a IS*¹ 1 Fine Monomer IUrethane Polymer AABBB Used (70) Particles (15) and Compound II (5) 1(5) PI*² (3) I (2) Example 21b IS*¹ 2 Fine Monomer II Urethane Polymer IABBBB Used (70) Particles (15) and Compound (5) 3 (5) PI*² (3) II (2)Example 21c IS*¹ 3 Fine Monomer I Urethane Polymer AABBB Used (70)Particles (15) and Compound II (5) 5 (5) PI*² (3) III (2) Example 21dIS*¹ 4 Fine Monomer II Urethane Polymer I AAAAA Used (70) Particles (15)and Compound (5) 7 (5) PI*² (3) I (2) Example IS*¹ 5 Fine Monomer IUrethane Polymer AABBB Used 21e (70) Particles (15) and Compound II (5)7 (5) PI*² (3) II (2) Example IS*¹ 6 Fine Monomer II Urethane Polymer IAABBB Used 21f (70) Particles (15) and Compound (5) 8 (5) PI*² (3) III(2) Example IS*¹ 1 Fine Monomer I Urethane Polymer AABBB Not Used 21g(70) Particles (15) and Compound II (5) 1 (5) PI*² (3) I (2) ExampleIS*¹ 2 Fine Monomer II Urethane Polymer I ABBBB Not Used 21h (70)Particles (15) and Compound (5) 3 (5) PI*² (3) II (2) Example IS*¹ 3Fine Monomer I Urethane Polymer AABBB Not Used 21i (70) Particles (15)and Compound II (5) 5 (5) PI*² (3) III (2) Example IS*¹ 4 Fine MonomerII Urethane Polymer I AAAAA Not Used 21j (70) Particles (15) andCompound (5) 7 (5) PI*² (3) I (2) Example IS*¹ 5 Fine Monomer I UrethanePolymer AABBB Not Used 21k (70) Particles (15) and Compound II (5) 7 (5)PI*² (3) II (2) Example IS*¹ 6 Fine Monomer II Urethane Polymer I AABBBNot Used 21l (70) Particles (15) and Compound (5) 8 (5) PI*² (3) III (2)Inspection Results Warpage and Shrinkage Reproducible PatternMisalignment Distortion (%) Pattern 1 Pattern 2 (μm) Example 21a NotObserved 0.2 100 μm or more 100 μm or more 2.1 Example 21b Not Observed0.03 100 μm or more  50 μm or more 1.9 Example 21c Not Observed 1.03  50μm or more 100 μm or more 0.9 Example 21d Not Observed 0.07 150 μm ormore  50 μm or more 2.2 Example 21e Not Observed 0.1  50 μm or more  50μm or more 2.8 Example 21f Not Observed 0.07  50 μm or more  50 μm ormore 1.6 Example 21g Not Observed 17.2 150 μm or more 250 μm or more 4.6Example 21h Not Observed 16.9 100 μm or more 100 μm or more 5.3 Example21i Partly Observed 15 200 μm or more 150 μm or more 3.6 Example 21j NotObserved 19.3 150 μm or more 100 μm or more 4.6 Example 21k Not Observed16.8 100 μm or more 100 μm or more 5.5 Example 21l Not Observed 14.3 100μm or more 100 μm or more 7.6

Examples 22a to 22g

[0335] Evaluation was made for trimmed ceramic substrates prepared byvarying the content of inorganic particles in the photosensitive ceramiccomposite. Test items and results are shown in Table 9, which shows thatserious distortion and warpage occurring in the firing step cause adeterioration in the pattern shape and the preciseness of alignment whenthe content of the inorganic particles is less than about 70% by weight.In contrast, when the content of the inorganic particles is more thanabout 93% by weight, a large number of cracks are formed in thesubstrates in the stacking step and/or the firing step, that is, uniformsubstrates cannot be prepared, because the content of an organiccomponent is too small to maintain the sheets flexible. Thus, in orderto precisely trim the substrates prepared using the photosensitiveceramic composite, the content of the inorganic particles is preferablywithin a range of 72% to 95% on a weight basis. TABLE 9 ManufacturingConditions Composition of Inorganic Components Inorganic Composition ofInorganic Fine Organic Components Particles Particles ComponentComponent Component Content of and and 1 and 2 and 3 and InorganicContent Content Content Content Content Components Sheet (wt %) (wt %)(wt %) (wt %) (wt %) (wt %) Arrangement Example IS*¹ 6 Fine Monomer IUrethane Polymer 62 AABBB 22a (92) Particles (60) and Compound II (20) 8(8) PI*² (12) I (8) Example IS*¹ 6 Fine Monomer I Urethane Polymer 70AABBB 22b (92) Particles (60) and Compound II (20) 8 (8) PI*² (12) I (8)Example IS*¹ 6 Fine Monomer I Urethane Polymer 73 AABBB 22c (92)Particles (60) and Compound II (20) 8 (8) PI*² (12) I (8) Example IS*¹ 6Fine Monomer I Urethane Polymer 78 AABBB 22d (92) Particles (60) andCompound II (20) 8 (8) PI*² (12) I (8) Example IS*¹ 6 Fine Monomer IUrethane Polymer 86 AABBB 22e (92) Particles (60) and Compound II (20) 8(8) PI*² (12) I (8) Example IS*¹ 6 Fine Monomer I Urethane Polymer 93ABBBB 22f (92) Particles (60) and Compound II (20) 8 (8) PI*² (12) I (8)Example IS*¹ 6 Fine Monomer I Urethane Polymer 97 AABBB 22g (92)Particles (60) and Compound II (20) 8 (8) PI*² (12) I (8) InspectionResults Warpage and Shrinkage Reproducible Pattern MisalignmentDistortion (%) Pattern 1 Pattern 2 (μm) Example Seriously Not Measurable500 μm or more 500 μm or more Not 22a Warped Measurable Example Warped3.5  100 μm or more  50 μm or more 4.6 22b Example Slightly 2.2   50 μmor more 100 μm or more 2.3 22c Distorted Example Not Observed 0.07  50μm or more  50 μm or more 0.6 22d Example Not Observed 0.04  50 μm ormore  50 μm or more 1.1 22e Example Partly 0.03  50 μm or more  50 μm ormore 1.6 22f Warped Example Cracked Not Measurable 300 μm or more NoneNot 22g Measurable

Examples 23a to 23n

[0336] Investigation was made for the correlation between trimmingaccuracy and the content of fine particles in inorganic particlescontained in the photosensitive ceramic composite. In order toinvestigate the effect of a change in the average particle size of thefine particles, part of the alumina particles, of which the content inInorganic Sub-component 6 is 52% by weight, were replaced with aluminafine particles.

[0337] Test items and results are shown in Table 10, which shows thatdistortion occurs when the content of the alumina fine particles in theinorganic particles is less than 5% by weight. When the content of thealumina fine particles is within a range of 5% to 25% on a weight basis,distortion hardly occurs and the sheets can be precisely trimmed by thephotolithographic process. When the content is more than 25% by weight,the substrates obtained by firing have cavities therein becauseaggregation occurs in the photosensitive ceramic composite. Terefore,uniformity of the substrate stracture got worse. It caused thedetorioration of the accuracy in trimming and alignment. Thus, when thecontent of the alumina fine particles in the inorganic particles iswithin a range of 5% to 25% on a weight basis, the ceramic substrates,precisely trimmed, having a satisfactory density can be obtained. TABLE10 Manufacturing Conditions Composition of Inorganic Organic ComponentsComponents Component Component Component Content of Glass Alumina IFP*³and 1 and 2 and 3 and Inorganic Content*¹ Content*² Content ContentContent Content Components Sheet (wt %) (wt %) (wt %) (wt %) (wt %) (wt%) (wt %) Arrangement Example 23a 48 52 Not Used Monomer I UrethanePolymer 80 AABBB (60) and Compound II (20) PI*⁴ (12) I (8) Example 23b48 50 IFP*³ 7 Monomer I Urethane Polymer 80 AABBB (2) (60) and CompoundII (20) PI*⁴ (12) I (8) Example 23c 48 45 IFP*³ 7 Monomer I UrethanePolymer 80 AABBB (7) (60) and Compound II (20) PI*⁴ (12) I (8) Example48 37 IFP*³ 7 Monomer I Urethane Polymer 80 AABBB 23d (15) (60) andCompound II (20) PI*⁴ (12) I (8) Example 48 30 IFP*³ 7 Monomer IUrethane Polymer 80 AABBB 23e (22) (60) and Compound II (20) PI*⁴ (12) I(8) Example 23f 48 25 IFP*³ 7 Monomer I Urethane Polymer 80 AABBB (27)(60) and Compound II (20) PI*⁴ (12) I (8) Example 23g 48 21 IFP*³ 7Monomer I Urethane Polymer 80 AABBB (31) (60) and Compound II (20) PI*⁴(12) I (8) Example 48 52 Not Used Monomer I Urethane Polymer 80 AABBB23h (60) and Compound II (20) PI*⁴ (12) I (8) Example 48 50 IFP*³ 8Monomer I Urethane Polymer 80 ABBBB 23i (2) (60) and Compound II (20)PI*⁴ (12) I (8) Example 48 45 IFP*³ 8 Monomer I Urethane Polymer 80AABBB 23j (7) (60) and Compound II (20) PI*⁴ (12) I (8) Example 48 37IFP*³ 8 Monomer I Urethane Polymer 80 AABBB 23k (15) (60) and CompoundII (20) PI*⁴ (12) I (8) Example 23l 48 30 IFP*³ 8 Monomer I UrethanePolymer 80 AABBB (22) (60) and Compound II (20) PI*⁴ (12) I (8) Example23m 48 25 IFP*³ 8 Monomer I Urethane Polymer 80 AABBB (27) (60) andCompound II (20) PI*⁴ (12) I (8) Example 23n 48 21 IFP*³ 8 Monomer IUrethane Polymer 80 AABBB (31) (60) and Compound II (20) PI*⁴ (12) I (8)Inspection Results Warpage and Shrinkage Reproducible PatternMisalignment Distortion (%) Pattern 1 Pattern 2 (μm) Example 23a PartlyDistorted 0.04 100 μm or more 100 μm or more 1.2 Example 23b PartlyDistorted 3.5 100 μm or more 100 μm or more 1.1 Example 23c Not Observed1.4  50 μm or more 100 μm or more 0.9 Example 23d Not Observed 0.07  50μm or more  50 μm or more 0.24 Example 23e Not Observed 0.04  50 μm ormore  50 μm or more 0.6 Example 23f Not Observed 1.5 100 μm or more 200μm or more 1.1 Example 23g Many Cavities 2.2 300 μm or more 500 μm ormore 1.6 Example 23h Partly Distorted 0.9 100 μm or more 100 μm or more1.2 Example 23i Not Observed 0.43 100 μm or more 100 μm or more 0.8Example 23j Not Observed 0.2  50 μm or more 100 μm or more 0.7 Example23k Not Observed 0.04  50 μm or more  50 μm or more 0.1 Example 23l NotObserved 0.03  50 μm or more  50 μm or more 0.4 Example 23m Not Observed0.8  50 μm or more  50 μm or more 1.6 Example 23n Not Observed 1.6 100μm or more 100 μm or more 2.7

Examples 24a to 24i

[0338] Investigation was made for the change in the viscosity of asolution used in the step of forming the photosensitive ceramiccomposite into sheets. Test items and results are shown in Table 7. Inevery sample, the results show that the square portions having area of50 μm or more in Pattern 1 or 2 can be formed by trimming with highreproducibility. Table 11 shows that serious warpage and the change insheet thickness cause a deterioration in the preciseness of alignment,local cracks, and strain when the viscosity of slurry or paste used inthe sheet-forming step is less than about 5 Pa·s or more than 100 Pa·s.When the viscosity is within a range of about 5 to 100 Pa·s, distortionhardly occurs and the ceramic substrates trimmed precisely can thereforebe obtained. A cross section of a sample prepared in Example 7a wasobserved with an electron probe X-ray microanalyzer. The analysis showedthat the alumina particles are locally aggregated and concentrated atboundaries between the sheets and the carrier film. TABLE 11Manufacturing Conditions Composition of Inorganic Organic ComponentsComponents Component Component Component Content of Glass Alumina IFP*³and 1 and 2 and 3 and Inorganic Viscosity Content*¹ Content*² ContentContent Content Content Components of Paste (wt %) (wt %) (wt %) (wt %)(wt %) (wt %) (wt %) (Pa · s) Example 24a 48 37 IFP*³ 8 Monomer IUrethane Polymer 80 1.5 (15) (60) and Compound II (20) PI*⁴ (12) I (8)Example 24b 48 37 IFP*³ 8 Monomer I Urethane Polymer 80 3.9 (15) (60)and Compound II (20) PI*⁴ (12) I (8) Example 48 37 IFP*³ 8 Monomer IUrethane Polymer 80 5.4 24c (15) (60) and Compound II (20) PI*⁴ (12) I(8) Example 48 37 IFP*³ 8 Monomer I Urethane Polymer 80 25 24d (15) (60)and Compound II (20) PI*⁴ (12) I (8) Example 48 37 IFP*³ 8 Monomer IUrethane Polymer 80 55 24e (15) (60) and Compound II (20) PI*⁴ (12) I(8) Example 48 37 IFP*³ 8 Monomer I Urethane Polymer 80 79 24f (15) (60)and Compound II (20) PI*⁴ (12) I (8) Example 48 37 IFP*³ 8 Monomer IUrethane Polymer 80 106 24g (15) (60) and Compound II (20) PI*⁴ (12) I(8) Example24h 48 37 IFP*³ 8 Monomer I Urethane Polymer 80 205 (15) (60)and Compound II (20) PI*⁴ (12) I (8) Example 24i 48 37 IFP*³ 8 Monomer IUrethane Polymer 80 320 (15) (60) and Compound II (20) PI*⁴ (12) I (8)Manufacturing Inspection Results Conditions Warpage and ShrinkageMisalignment Sheet Arrangement Distortion (%) (μm) Example 23a AABBBSeriously Warped Not Not measurable measurable Example 23b AABBB PartlyDistorted 0.15 4.6 Example 23c AABBB Partly Distorted 0.1 1.3 Example23d AABBB Not Observed 0.04 0.12 Example 23e AABBB Not Observed 0.040.09 Example 23f AABBB Not Observed 0.04 0.1 Example 23g AABBB NotObserved 0.04 0.6 Example 23h AABBB Uneven Thickness 0.12 0.9 Example23i AABBB Uneven Thickness 0.32 1.3

Examples 25a to 25e

[0339] Investigation was made for the correlation between the trimmingaccuracy and the particle size of the inorganic particles contained inthe photosensitive ceramic composite. Test items and results are shownin Table 12. The accuracy of photolithographic trimming is low when theparticle size of the fine particles is more than about 50 nm, as shownin Table 12. In contrast, when the particle size is about 10 nm,cavities are locally present and the aggregation is suppressed due to anincrease in the surface area of the inorganic particles. Thus, theparticle size is preferably about 5 nm or more. TABLE 12 ManufacturingConditions Composition of Inorganic Organic Components ComponentsComponent Component Component Content of Glass Alumina IFP*³ and 1 and 2and 3 and Inorganic Content*¹ Content*² Content Content Content ContentComponents Sheet (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %)Arrangement Example 48 37 IFP*³ 7 Monomer I Urethane Polymer 80 ABBBB25a (15) (60) and Compound II (20) PI*⁴ (12) I (8) Example 48 37 IFP*³ 8Monomer I Urethane Polymer 80 ABBBB 25b (15) (60) and Compound II (20)PI*⁴ (12) I (8) Example 48 37 IFP*³ 9 Monomer I Urethane Polymer 80ABBBB 25c (15) (60) and Compound II (20) PI*⁴ (12) I (8) Example 48 37IFP*³ 10 Monomer I Urethane Polymer 80 ABBBB 25d (15) (60) and CompoundII (20) PI*⁴ (12) I (8) Example 48 37 IFP*³ 11 Monomer I UrethanePolymer 80 ABBBB 25e (15) (60) and Compound II (20) PI*⁴ (12) I (8)Inspection Results Warpage and Shrinkage Reproducible PatternMisalignment Distortion (%) Pattern 1 Pattern 2 (μm) Example SmallNumber of 0.08  50 μm or more  50 μm or more 0.12 25a Cavities ExampleNot Observed 0.04  50 μm or more  50 μm or more 0.12 25b Example NotObserved 0.04  50 μm or more  50 μm or more 0.12 25c Example NotObserved 0.04  50 μm or more 100 μm or more 0.12 25d Example NotObserved 0.91 100 μm or more 100 μm or more 0.12 25e

Examples 26a to 26g

[0340] Investigation was made for the composition of the inorganic fineparticles contained in the photosensitive ceramic composite. Test itemsand results are shown in Table 13. In all the types of the fineparticles that are different in composition, trimming properties in thesame level can be obtained as shown in Table 13. In the X-ray analysisof the sintered samples, positions of diffraction peaks assigned toindividual crystal structures and the peak width at half height showthat there is no change in crystal structure in the samples. TABLE 13Manufacturing Conditions Composition of Inorganic Components InorganicComposition of Inorganic Fine Organic Components Particles ParticlesComponent Component Component and and 1 and 2 and 3 and Content ContentContent Content Content Sheet (wt %) (wt %) (wt %) (wt %) (wt %)Arrangement Example IS*¹ 1 Fine Monomer I Urethane Polymer I BABBB 26a(70) Particles (15) and Compound (5) 3 (5) PI*² (3) I (2) Example IS*¹ 1Fine Monomer I Urethane Polymer I ABBBB 26b (70) Particles (15) andCompound (5) 9 (5) PI*² (3) I (2) Example IS*¹ 1 Fine Monomer I UrethanePolymer I ABBBB 26c (70) Particles (15) and Compound (5) 12 (5) PI*² (3)I (2) Example IS*¹ 1 Fine Monomer I Urethane Polymer I AABBB 26d (70)Particles (15) and Compound (5) 13 (5) PI*² (3) I (2) Example IS*¹ 1Fine Monomer I Urethane Polymer I BBBBB 26e (70) Particles (15) andCompound (5) 14 (5) PI*² (3) I (2) Example IS*¹ 1 Fine Monomer IUrethane Polymer I ABBBB 26f (70) Particles (15) and Compound (5) 15 (5)PI*² (3) I (2) Example IS*¹ 1 Fine Monomer I Urethane Polymer I AABBB26g (70) Particles (15) and Compound (5) 16 (5) PI*² (3) I (2)Inspection Results Warpage and Shrinkage Reproducible PatternMisalignment Distortion (%) Pattern 1 Pattern 2 (μm) Example NotObserved 0.4 100 μm or 100 μm or 2.1 26a more more Example Not Observed0.4 100 μm or 100 μm or 1.6 26b more more Example Not Observed 0.41 100μm or 100 μm or 1.6 26c more more Example Not Observed 0.35 100 μm or100 μm or 2.1 26d more more Example Not Observed 0.32 100 μm or 100 μmor 2.6 26e more more Example Not Observed 0.29 100 μm or 100 μm or 1 26fmore more Example Not Observed 0.4 100 μm or 100 μm or 2.1 26g more more

Example 27

[0341] A dielectric patch antenna was prepared using the sample obtainedin Example 18d. The reflectivity thereof was measured using a networkanalyzer. The same preparation and measurement as the above were madefor the sample, prepared in Comparative Example 1, punched with the die.As a result, both samples had a resonant frequency of 2.45 GHz; however,the sample prepared by the photolithographic process had a band width of±17 MHz and the sample prepared by the punching process had a band widthof ±55 MHz.

[0342] (4) Preparation of Photosensitive Ceramic Composite ContainingOrganic Component, Containing Low Refractive Index Sub-component, HavingOptimized Flexibility, Compatibility, and Developability and Preparationof Multilayer Substrate Containing the Composite

Example 28

[0343] A photosensitive ceramic composite was prepared using theinorganic-particle source material, used in Example 1 of Item (1),containing particles having the SiO₂ layers with a thickness of 70 nmand the photosensitive organic component, used in Example 5 of Item (2),containing Polymer I (15%), Urethane Compound I (2%), Monomer I (5%),and the photopolymerization initiator. A sample for evaluating the lighttransmittance was prepared in the same manner as that described in Item(1). The measurement showed that the sample has a total beamtransmittance of 65% and a rectilinear beam transmittance of 7.8%. Thecomposite was formed into green sheets having a thickness of 100 or 150μm. The formation of via-holes was attempted, and 40-μm via-holes wereobtained. In a step of developing the sheets, a solution having thefollowing composition was used: the same composition as that ofDeveloping Solution I used in Example 5 of Item (2). The photosensitiveorganic component had a haze of 0.1. The change in line width was 1.2.The obtained green sheets were cured and then placed between aluminabinding sheets. The resulting green sheets were fired at 900° C. for 30minutes, whereby a multilayer substrate. The multilayer substrate had nocracks but had a bending structure of 270 MPa and a dielectric constantof 7.8 (1 MHz). The cured green sheets had a tensile strength of 0.6N/mm2 and an elongation of 20%.

[0344] The green sheets were trimmed in the same manner as thatdescribed in Example 18 of Item (3), whereby a white multilayersubstrate was prepared. In the trimming step, for Patterns 1 and 2described in Example 18 of Item (3), the square portions having a sizeof at least 100 μm square or more were formed. The substrate had nowarpage.

[0345] A dielectric patch antenna was prepared using this sample. Thereflectivity thereof was measured using a network analyzer. The samplehad a resonant frequency of 2.45 GHz and a band width of ±12 MHz.

Industrial Applicability

[0346] According to the present invention, ceramic-substrate sourcematerials in which fine structures having a high aspect ratio can beformed can be prepared using a photosensitive organic componentcontaining inorganic particles, as described above. Since distortion andthe like do not occur in sheets containing the composite in preparingsteps, fine processing properties and high reproducibility can beachieved.

[0347] A ceramic multilayer substrate having an arbitrary outer shapecan be prepared with high reproducibility using the composite of thepresent invention, the shape being formed by trimming sheets by aphotolithographic process.

1. A photosensitive ceramic composite containing inorganic particles anda photosensitive organic component, wherein the inorganic particles haveat least surface sections containing an inorganic material having arefractive index less than that of inner sections of the inorganicparticles.
 2. The photosensitive ceramic composite according to claim 1,wherein the formula 5≦t ≦200 (nm) is satisfied, where t represents thethickness of the sections containing the low-refractive index material.3. The photosensitive ceramic composite according to claim 1, whereinthe following formulas are satisfied: 0.05≦R1−R2−0.15≦R2−R3 where R1represents the refractive index of the inner sections of the inorganicparticle, R2 represents the refractive index of the low-refractive indexmaterial, and R3 represents the refractive index of the photosensitiveorganic component.
 4. The photosensitive ceramic composite according toclaim 1, wherein the formula 1.1≦ST1/ST2 is satisfied, where ST1represents the rectilinear beam transmittance of the photosensitiveceramic composite and ST2 represents the rectilinear beam transmittanceof the photosensitive ceramic composite that does not have the sectionscontaining the low-refractive index material.
 5. The photosensitiveceramic composite according to claim 1, wherein the low-refractive indexmaterial contains at least one selected from the group consisting ofZnS, CeF₂, MgF₂, and SiO₂.
 6. The photosensitive ceramic compositeaccording to claim 1, wherein the shrinkage in the X-Y plane is 1% orless before and after a firing step and the formula N1−N2 ≦0.15 issatisfied, where N1 represents the refractive index of a componenthaving a maximal refractive index and N2 represents the refractive indexof a component having a minimal refractive index.
 7. The photosensitiveceramic composite according to claim 1, wherein the inorganic particlescontain at least one selected from the group consisting of alumina,zirconia, magnesia, beryllia, mullite, spinel, forsterite, anorthite,celsian, and aluminum nitride.
 8. The photosensitive ceramic compositeaccording to claim 1, wherein the inorganic particles contain a compoundrepresented by the formula R_(x)O—Al₂O₃—SiO₂, where R represents analkali metal when x=2 and or R represents an alkaline-earth metal whenx=1.
 9. The photosensitive ceramic composite according to claim 1,wherein the inorganic particles are a mixture containing 50% to 90% ofglass particles and 10% to 50% of quartz particles and/or amorphoussilica particles on a weight basis.
 10. The photosensitive ceramiccomposite according to claim 1, wherein the inorganic particles are amixture containing 30% to 60% of borosilicate glass particles, 20% to60% of quartz particles and/or amorphous silica particles, and 20% to60% of ceramic particles containing at least one selected from the groupconsisting of spinel, forsterite, anorthite, and celsian on a weightbasis.
 11. The photosensitive ceramic composite according to claim 1,wherein the inorganic particles are a mixture containing 30% to 60% ofglass particles and 40% to 70% of ceramic particles containing at leastone selected from the group consisting of alumina, zirconia, magnesia,beryllia, mullite, spinel, forsterite, anorthite, celsian, and aluminumnitride, and the glass particles contain 85% or more of oxides and havea SiO₂ content of 30% to 70%, an Al₂O₃ content of 5% to 40%, a CaOcontent of 3% to 25%, and a B2O₃ content of 3% to 50% on a weight basis.12. The photosensitive ceramic composite according to claim 1, whereinthe photosensitive organic component contains an acrylic copolymerhaving side chains with a carboxyl group, a photoreactive compound, anda photopolymerization initiator.
 13. The photosensitive ceramiccomposite according to claim 1, wherein the content of thephotosensitive organic component ranges from 10% to 40% on a weightbasis.
 14. The photosensitive ceramic composite according to claim 1having a dimensional change of 1 to 1.5 in a developing step andcontaining the inorganic particles (component B) and the photosensitiveorganic component (component A) containing a (meth)acrylate compound(sub-component A1) represented by the following formula and a urethanecompound (sub-component A2) having an ethylenic unsaturated group:CH₂═CR¹COO—(R²)_(n)—R³—R⁰   (1) wherein R⁰ represents aCH₂═CR¹COO—(R²)_(n)—group, a hydrogen atom, or a halogen atom; R¹represents a hydrogen atom or a methyl group; R² represents an alkyleneoxide group or an alkylene oxide oligomer group; R³ represents a cyclicor acyclic group selected from the group consisting of an alkylenegroup, an aryl group, an aryl ether group, an arylene group, an aryleneether group, an aralkyl group, and an aralkylene group having 1 to 15carbon atoms or represents such a cyclic or acyclic group having asubstituent such as an alkyl group having 1 to 9 carbon atoms, a halogenatom, a hydroxy group, or an aryl group; and n represents an integer of1 to
 5. 15. The photosensitive ceramic composite according to claim 14,wherein the group represented by R³ in formula (1) has at least onearomatic ring.
 16. The photosensitive ceramic composite according toclaim 14, wherein the group represented by R² in formula (1) has atleast one ethylene oxide group.
 17. The photosensitive ceramic compositeaccording to claim 14, wherein the sub-component A1is para-cumylphenol(meth)acrylate modified with ethylene oxide.
 18. The photosensitiveceramic composite according to claim 14, wherein the sub-component A2 isa urethane compound represented by the following formula (2):CH₂═CX₁COO—X²—(X³—X⁴ )_(n)—X³—X²—OCOCX¹═CH₂   (2) wherein X¹ representshydrogen, a hydroxy group, or a methyl group; X² and X⁴ each representan alkylene oxide group or an alkylene oxide oligomer group; at leastone of the group represented by X² and the group represented by X⁴ hasan ethylene oxide group; X³ represents an aliphatic diisocyanate residueor a cycloaliphatic diisocyanate residue having a urethane bond; and nrepresents an integer of 1 to
 10. 19. A method for manufacturing amultilayer substrate using the photosensitive ceramic compositecontaining the inorganic particles and photosensitive organic componentaccording to claim 1, comprising: (1) a step of forming thephotosensitive ceramic composite into photosensitive green sheets; (2) astep of trimming the resulting photosensitive green sheets by aphotolithographic process; (3) a step of stacking the resultingphotosensitive green sheets; and (4) a step of firing the resultingphotosensitive green sheets.
 20. A method for manufacturing a multilayersubstrate using the photosensitive ceramic composite containing theinorganic particles and photosensitive organic component according toclaim 1, comprising: (1) a step of forming the photosensitive ceramiccomposite into photosensitive green sheets, the sheets being placed on acarrier film; (2) a step of trimming the photosensitive green sheetsplaced on the carrier film such that the photosensitive green sheetshave isolated portions; (3) a step of separating the photosensitivegreen sheets having the isolated portions from the film to stack theresulting sheets; and (4) a step of firing the stacked photosensitivegreen sheets.
 21. A multilayer substrate manufactured by the methodaccording to claim 20.